happened to me on another casino and i didn’t just accept it. Put in a formal complaint to show the t&cs are prohibitive and threaten IBAS.
They will fight with you every step of the way and it isn’t an overnight fix.
Get them to admit you are at deadlock if they won’t back down so you can take to IBAS. If you are with a casino that has a UK licence they do rule in your favour on this type of thing more often than you would expect (its almost like they want to rule against casinos).
Check the t&cs on the site as many of them have t&cs which contradict each other which means they are prohibitive and open to interpretation. I once had a dispute with a big casino which had t&cs templated/ copied from another casino in the same group- they were unenforceable as they didn’t even have the correct name of the casino on them (screen shotted and saved obviously).
Always stay polite and professional in your complaints and make sure everything is in writing every step of the way. If they want to discuss with you on the phone which they may do at the latter stages of complaint make sure you record the call (and legally you have to say at the start of the call you are recording it).
Don’t just accept it- fight it. at the very worst they will want to settle on some amount with you.
Took six months but I got paid.