In fact, if you look at TaC metaspins.com then you can see that there is a very small list of limited territories that include countries such as Afghanistan, Cuba, Curacao, Cyprus, Iran, Iraq, Isle of Man, Italy, Malta, Netherlands and its territories, North Korea, Belarus, Spain, Sudan, Syria, United Kingdom and its territories, United States. But if they refer to a violation of the rules of one account- one IP, then it is possible that the player logged into the account, for example, using another provider and, for example, from a mobile phone, and if the player has a dynamic IP, what to do in this case, of course, they may identify the device itself by mac address.
We either don't know all the facts here or the casino is at fault. At least that's my understanding of the case.
Even if player had another account, he had a decent deposit of 420 USD and a big win of 9000 USD. OP won at slots which means it had nothing to do with a different IP address or another account, even if he is guilty of that.
They could ban his account and return the deposit, but they chose to be greedy and steal everything. Also it looks really shitty because they did nothing until he won. Then they contacted him about KYC and then came up with the idea to steal his deposit. If he was changing IPs then it should have been obvious from the start. Why ask him for KYC then?
From what I can see here they were hoping he wouldn't give them his ID but since he did everything right with KYC they came up with a fraud charge.
If OP was making multiple accounts and claiming bonuses that he tried to withdraw and disappear, they would have the right to do what they did, but it doesn't seem like the bonus, or another account had anything to do with his win in slots.
Metaspins should provide a solid proof against OP and explain why his deposit wasn't returned. Another IP or another account from the same IP doesn't justify stealing a deposit.