I've applied to a good programme (lets call it A) and when i did not hear from them for a month I've applied to another uni (B) which is much higher in rankings. University (B) sent an offer but didn't give me any scholarships, since i didn't hear from the others I accepted B's offer. The assigned supervisor never contacted me, it was always the law school assistants who emailed me.
Then Uni (A) contacted me and sent tons of suggested amendments, soon after a professor contacted me and said i should amend some parts and we can have an interview online. (This professor supervised the phd of the one from Uni B - thats how experienced she is...) My other friends, who are doing their PhDs, told me to be honest so I replied and said I am very interested in Uni (A), but I have already accepted another university and that I would still apply for Uni (A) scholarships, I also sent her the amended proposal... Since then 3 weeks have passed and I think she will never reply.
Then another university said my proposal needs amendments too so now I feel like my initial proposal was awful and I'm wondering what is wrong with Uni (B) for accepting me so quickly although it is clearly more prestigious than the others? Is it possible they take international students without much consideration to receive more money? Should I have lied to Uni (A) about the other programme? What should I do?

This is a case where honesty is not the best policy. I really believe in looking after your own self-interests in these cases, but anyway...

I think uni A hasn't replied because you have already accepted B's offer. You should probably email to check though.

I'm sure your research proposal was fine, but remember everything can be improved and these supervisors know far more than you do.

As to whether universities just take any international student that comes with money? They certainly do. In my research group there are 6 international students that are funded by their governments. Not a single one had to have an interview - they were accepted straight away regardless of the content and quality of their research proposal.

Have you got your own funding? If yes, just select the university that has accepted you. If not, accept any offers you get and apply for funding. Then you can have your pick if you get any funding.

So do you think i should contact the supervisor from Uni A and say something like i would still accept your offer even without funding or would it be too weird? I'm also afraid its too late since they already know about the other university.

I would just email them and ask if there is any progress on the amended proposal that you sent. I wouldn't mention funding. Just say you are still interested in the offer of an interview and give the reasons why you want to try for that place. Try not to sound desperate but remain confident.
It sounds like the supervisor at Uni A would have heard about your application to Uni B in the end anyway, (if they supervised that person's PhD), so I wouldn't spend too much time worrying about being honest.
Its done now anyway, and you can't change that, so best to look forward and deal with the situation as it is. Try not to panic, sometimes the best way to learn these kind of things is to make a small mistake and stay professional whilst trying to solve it. Best of luck to you anyway.

Your situation sounds very similar to mine. I applied to one uni (very good dept but lesser ranked overall) it had no funding, I accepted. Then another uni better ranked overall but the dept wasn't as good as the other offered funding. It became clear that I needed funding so withdrew from the other uni and accepted the funded place. Academia is pretty incestuous, depts across universities often have links and I expect the issue of accepting unfunded places which are then turned down for scholarship elsewhere is pretty common considering how they do the applications so ad hoc. I wouldn't worry yourself too much about it. Hope the amended proposal goes well :D

So if i send an email and say i'm more interested in their programme and if they reject/do not reply, wouldn't it be very bad if my new supervisor hears about it? I'm trying to find the right place but i'm not used to these things.. I wish I was funded by an external source so I could apply to all universities and choose the best one.

It's very difficult to judge human reactions but my thoughts are, if the supervisors know each other you might crop up in their conversation. As uni A supervised uni B, telling them that B accepted you might show A you are a credible candidate (like a recommendation).

The uni I turned down were very understanding. I just told them my circumstances had changed and whilst I thought I could progress with an unfunded place, funding was now a requirement to my completing a PhD. The supervisor just wished me the best of luck. But that's my story and other supervisors might take it differently.

Uni A replied my last email and told me they would only interview me if i havent accepted another place. I was trying to prepare a polite email to tell them that i have accepted elsewhere (as i mentioned before) and only wanted to see if their programme was a better fit for me and was going to apologise for taking their time. before I could send that email, Uni A co-supervisor emailed me and gave me the date for the skype interview. Should i go ahead with the interview or tell them about the other place in an email? I told them that before and the fact that they told me they would interview me only if i havent accepted another place made me think it was pointless. Now this skype interview offer confused me..

Personally, I would wait for the interview since they already scheduled it. You can see how it goes; if you think Uni A could work out and you have a good feeling about the interview, you should mention it at the end (explain briefly what happened, why you went for Uni B and that Uni A would still be your first choice).
I do not see you as wasting their time either. As a university, of course I would make sure that the student is still interested (i.e. has no PhD position yet). But in your case you definitely are interested despite already having a position.