withdawal funds

I recently won £2000.00 on gnuf casino ihave deposited on there in the past . i recived a email saying i had free spins in my account . I was made up you don't get many brucy bonuses like that . They gave me 25 free spins on the gold factory i fortunatly got a good win wich gave me over a £100 i was made up . I played on a variety of slots and got up to £200.00 i had already talked to the live chat and they said well done on my win they just needed to have a look at some id . I sent them a picture of my passport a letter with my adderess etc everything seem to be looking on the right track . I have just recived a email from them saying i can only cash out a £100 and the rest has been confiscated they said the max cash out on the bonus was £100 . I wouldn't of minded if they had told me that in the first place but they never bi feel like i have been robbed i won that money fair and square and they have took it of me . Please can you help me