Assessment is a really a mathematically process. You should take out your School's and your University's Regulations handbook and work out where you stand with your marks. There are rounding up and rounding down rules, conceptual marking schemes and band grading possibilities. Having 58 is not close to have a merit. Having 59.5 is.  Most Universities apply a rule that you need a 70 in the dissertation to get a distinction. The 67 is your dissertation may help your overall average in your hope to get a Merit as often the dissertation is a double weighted module. Having had 4 Ds in the first four modules it is very difficult to regain ground.

You cannot challenge the mark of a piece of academic work. This is wasted effort.You can only challenge the circumstances of the assessment. The main grounds are (1) lack of adequate supervision and (2) procedural irregularities.  In terms of extenuating circumstances, check your regulations to see where your circumstances fall. Again, if the reason is minor, and you were granted a few days leave, or an extension to hand in some work, it is unlikely that this could help you.

Often having a Masters - regardless of the grade - is the criteria for jobs. The grade is often less important, unless you are planning to apply for a PhD. You can easily explain the Pass grade, by saying - I was working full-time and had to fit the Masters in alongside my job. Therefore the mark does not reflect my true ability.

Hope this helps. Be kind to yourself. Masters studies are a hard slog. I am sure your parents are pleased as punch that you got your Masters and are not as focussed on the classification as you think.