Have they blocked your account or can you still log in a place bets? If you can still log in, then they might be deliberately stalling in the hope that you will carry on betting and lose some or all of your funds. If this is what they are doing, then they wouldn't be the first bookmaker to behave in such a disreputable way. Under no circumstances should you bet with them again until they have paid you in full.
If you're based in the UK (and I assume that you are if your account is with the 'co.uk' arm of 10Bet), then at least you have the option of taking them to court if they continue to refuse to pay without good reason.
A lot of players like 10Bet, but personally I wouldn't touch them with a barge pole.
Has the amount (12k) you attempted to withdraw been returned to your account balance or has it been 'frozen' pending further developments? If it has been returned to the account balance so that you can continue gambling with it, then I don't think there is much doubt what they're trying to do. If - and I stress 'if' - they are deliberately withholding payment in the hope that you will continue to gamble on their site and lose your winnings, then that would represent a very serious breach of responsible gambling standards.
They have website as well - www.resolver.co.uk - although it wasn't immediately clear to me whether they intervene on your behalf or simply provide advice on what steps you should take yourself (I think it might be the latter). I've never used them myself.