As a Union Official I would advise to you to get on to your Union today.   If anything like this happens it must be reported, in writing, immediatley. It's a pretty poor school that let's a situation like this go by and does nothing about it, although I am only speaking about the uk and cannot comment on anywhere else. We cannot help over the net, you must get your Union's legal department on to it now or you stand to lose so much. If you don't belong to a Union then go to a solicitor and get proper advice as a union is not allowed to work on cases retrospectively, before you were a member. Good luck.