Re: I did very serious mistake. Sent USDT to USDC address.

Thanks you for your suggestion. I sent the 10K USDT to the USDC Coinbase Commerce merchant account for the goods and merchant told me that they have mnemonic phase of wallet, There is any possibility to recover from there?

It's guaranteed that they will have the private keys of the wallet. The question is, if they will go out of their way to help you or not. Because it's not just as simple as grabbing the private keys and importing it to MEW and sending you the funds.

Since 10k is a good amount of money though, I'm guessing that they'll probably help you.

My merchant (Payment receiver) have mnemonic phase, Can he recover from his side?

Again like I said, yes they can, but the question is: will they? Because we're talking about Coinbase here, a behemoth of an exchange; not just some friend of yours. Some exchanges requires a minimum amount for them to actually bother recovering your money. It's just up to Coinbase if they'll help you, just respond to their questions.