It's not stake's fault when you lose a bet. It is entirely your fault. Maybe it was a bug since you didn't get ban from violating their rules or something like but a request made by you to self-excluded ban. Gambling sites are like that, when you ask them to ban temporary or permanent is you cannot deposit or withdraw on their site but in your case is you are able to deposit and bet. My guess is as stated above that it is bug/issue or you aren't ban yet.
Totally agree on this since we cannot blame the site if we lose are money because in the first place, its gambling and you should really understand the risk of it before you complain. Yes, you asked them to banned you from gambling but if you didn’t help yourself to stop thinking about it, you can still fall on that trap and that’s what happened to OP. Learn from it and commit to stop from gambling, don’t ever try to deposit on any site again so you wont blame them.