I had to get a new account because I had some trouble with multiple accounts over the past 10 years while I lived in different countries. I was forced to open multiple accounts by them not by my own choice. But never had my accounts frozen. Their customer service is actually very responsive, understanding and helpful in my personal experience. Got it all sorted over the phone after several chatting sessions. I explained the errors and they understood it. For withdrawal issues you have to prove your identity and go through some tax/fraud checks or declarations (the norm now) but not much else from what I can remember.
I had accounts banned without reason, proof or any chance to say something back at
Ladbrokes and Coral. So all I can do is advise against ever playing their poker. Also, many horror stories regarding their sports betting (which I don't do). All they do is give back your deposited money but none of the winnings, which thankfully I didn't have much of. Very long process to take them to court as you have to go through long-wait steps to report them to regulatory bodies and it takes months if not years, to get a useless reply and only then take them to court, which for minimal sums of money is not worth going through the trouble as you pay more than you'll ever get. For anything significant, I would have gone all the way. I simply wanted to recover my accounts more than anything eles, so I could keep playing and solicitors were asking for a few grand for the court process.
My advice is be open and chat with them. Of course, unless you are guilty of any wrong doing. Could there be misunderstandings? Could you have not intended to do something that was flagged in their system? Could there be an error in IT or human judgement? Good companies will accept and look into anything reasonable. Cowboys never will cause they don't care and should be avoided altogether.