So what should I do?
There is strength in numbers. One person needs to take a case to the High Court. If the High Court upholds that case, then the others can take cases of their own as the ruling of the High Court would set a precedent.
User Bungaro on Askaboutmoney has set up a group to take such a case.
Don't spend your €1,615. Send it to the group to fund the legal action. If the action is successful, you should get your money back. You should also get a cheap tracker backdated to when you came off the fixed rate. You should also get compensation for the distress caused by being overcharged.