Really sorry to hear that @OP, it's huge.

My suggestion is you need to contact MEXC support because they're centralized exchange, even though we can use it without KYC, but probably the hacker might have KYC-ed his account.

There was no mentioned they will freeze someone else coins and complying with the laws, so I doubt it. But that's what the real No KYC P2P exchange where they're freely to accept anyone to use their services.