I've noticed that there are
many complaints about the work of the Mercatox support team. Nevertheless, I think the only way you can solve the issue is through the pressure on the support team and posting complaints on the Mercatox social media pages (especially Twitter). If you want to use Metamask then it's their duty to assist you.
i dont think he can use metamask to use the wallet address from that exchange and they are the one who can send it back to the owner if ever.
The only option is to ask support if they can do that for you or else its gone, mercatox will own that token. If its true that its change the contract then you send different tokens in that exchange not the one you are sending.