What about Binance P2P?
and there is a member from Nigeria who is very trusted
CryptopreneurBrainboss, he have an exchange service, from Altcoins to Nigerian Bank Accounts, indeed it is not for the service you need but maybe with proportional fee he is willing to help you, just wanted to let you know, and also not knowing if withdrawing from a gambling site directly to a bank account in nigeria is safe, hope you can withdraw the money.
I find this interesting are all affiliates of BC.GAME have the same issue if they are not from Nigeria and you can withdraw your earnings using a Nigerian Bank only, quite unfair to affiliate like you if they only have this option, knowing this, will promoters will likely promote BC.game if the withdrawal option is limited to a Nigerian Bank, hope Brainboss can help you with this and do update us for the development of your case.