Hi Alisadixan
There is a reason why UK universities insist on an English language criteria as PhDs are not easy, and have to be written entirely in good English. Clearly you are very close to meeting the language criteria, so my advice would be quite simple, try again in a few months and you should be just fine. You say your English is improving day by day, so you should pass the test easily in a few months. I can see this being a problem if there are time limits being imposed by something eg contracts or visas and stuff, but really I would say just keep trying.