Corsa-B.uk - Vauxhall, Opel and Holden Corsa B Owners Club

i have taken a few stereos out of cars before and they can sometimes be a bit difficult but i have released the four clips on this one and its just not budging you don't even get a bit of movement i hadn't done corsa one before but they are normally all the same when it comes to removing a head unit. Does anybody know why it wont come out or if i am missing something really stupid, its an n reg corsa twist anyway. Please help me