I hope I'm wrong, but USDT addresses look pretty similar to BTC addresses. Are you sure you've sent to a BTC address and not USDT?

Please check make sure you've sent the Bitcoins to a Bitcoin (BTC) address. Polo clearly tells in red "please make sure you send only to this address".
I have a hunch that you've sent to an address Polo doesn't handle. Because I've never had such problems...

I really hope that I'm wrong....