What I don't get here is, you've shared your withdrawals page and you were able to withdraw about 500 ETH and even 500k USD around 2 times (or more) if I'm not wrong as we all can see that there's a transaction ID shown there.
Didn't they come and ask you these things the very first moment you tried to withdraw?
I mean, why now? When you have already withdrawn there so many times, then what's the issue?
I don't know Duelbit's threshold amount for KYC but they should have done that in the first withdrawal they let him on the second time but the third time they have to do it because there may be fourth or fifth withdrawals coming that are as huge as those withdrawals and since they are compliant to money laundering they have to stop and ask for the source of funds, OP should understand this is something that's going to come eventually.
The lesson here is if you're going to deposit and play a huge amount you have to back it up where the funds are coming now you have to be truthful on the source of funds and hopefully you pass their criteria.