I had a similar experience with an Exchange. After the Bullrun of 2017 and 2018 i had some of coins parked in Polo... I didnt log in in a while and after a few month i came back, just to see they had delisted a coin.
Well first of all, sure my part was the negligence to hold them on an Exchange after all. A total no go.
But the reason i was really annoyed was, that the exchange didn´t send any E-mail or information out to its customers.
That was a scatchy move.
I since then abandoned the exchange. I use coldstorage and just move coins for trades to an exchange i "trust".
Its time for some good DEX.

Greetings