Hi,
I'm from the UK and managed to get a sizeable refund/repayment some years ago.
You'll need to check with a solicitor, but basically the forms you sign waiving your rights to a refund are not legally binding in the UK. (At least they weren't when I did legal action).
How long ago are we talking about when you paid your money into the organisation? I ask because usually you only get 6 years in which to claim money taken from you under false pretences or by undue influence etc...... Again, you'll need to check with a solicitor.
IM me if you need any advice.