I think this is the best way too. Always transfer Bitcoin because that is the most stable blockchain network. Then within the platform just get the Tether or whatever you need.

You should also check USDT blockexplorer first, to see if really your tx made it and the address has a balance. Then contact the support, show all the proof and detailed transactions.

I also experience the same thing, but different markets, my suggestion is better you make direct contact to poloniex, via telegram or social media, and show proof of your transaction.