Well, check your wallets. It should be there, mine is there. If it's not, either you didn't hold NXT before october 12th, or polo fucked up. In that case, send a support ticket to Polo.

Sending your NXT won't send your Ardor "with them". They are separate now.

You can't send Ardor directly from Polo to Bittrex, at least you couldn't two days ago. I suspect that didn't change. So, to get Ardor from Polo to Bittrex, you need a Wallet, send them there, then to Bittrex.