That practice of disabling customer withdrawals (but allowing them to deposit and play when large winnings were due) used to be fairly wide spread until several years ago. I know some casinos/gaming websites still do it but nowadays it seems to be mentioned less whenever scam accusations are made. I think it is a practice Metaspins should not be engaging as it should have been stopped across the industry a long time ago.
At the same time, the casino also plays dirty by deactivating OP's withdrawal feature when he won big, then that restriction disappeared when he lost the balance, only to reappear when he won another big games. IIRC, they tried to defend themselves by saying that the previous blocking was followed by investigation, but OP said he never submitted any KYC documentation as they claimed they had asked him, and the restriction [evidently] got lifted by itself once he drained his fund.