1. It is not true, even if it was (we still did not receive a singe piece of proof), it was not intentional. 1 (one) transaction out of many hundreds, over the 2-3 years period.

I will let other people to decide if they want continue to use your service.

 Where are the rules of the service, that let you take users funds or impose such charges? Why are you trying to charge 3500 EUR, not 35 000 EUR or 350 000 EUR? I guess, if the balance would have been like 100k, your charges would be 200k. Play as you go, right?

Again, be extremely cautious dealing with this service, at any given time he has full access to your funds. If you had a positive experience so far, may be the reason is that you did not have enough funds there, yet.