Okay, so they need a Decree Nisi or a Letter from a solicitor, in which I have neither.
I called them up and they said I would need a council tax bill showing a 25% discount. So I got the two of them right now, one is for this year (2015/16) which does not show the discount as I am 18. I also have one for the year 2014/15 which shows the 25% discount. Is it possible that I give them the 2014/15 one? I find this BS as a lot of students would have turned 18 when doing this form..