I think he accessed the platform using VPN and the account was flagged and blocked, and now his winnings are stuck in there.
You might be right that op has been flagged and blocked for using VPN I am agree with this part too. But I am not too much optimistic, I think OP has been been banned for using multi account and/or abusing the system. And as OP has used multi account OP may tried to use vpn sothat the ip would not show same. I think it because op said:
Stake limited my betting because I was winning. They limit and froze my account because I was a winner and stake don't like winners.
no my account funds are frozen but I can still place bets. They limited my bets and not for multi account reasons