Maybe bittrex is still the best to date, I've been using bittrex for a long time and never had any problems there, that's what kept me going with bittrex. Some exchanges can still be to be recommended but still to be careful on all exchanges, as saving all the money on exchange is very risky.
Have you tried to register a new account? Here's what that page says:
"We are currently only accepting new account requests from our corporate customers and select invitees. We are excited to have so many new users who want to join the Bittrex community. To those that want to join our community, we will keep you posted on when we open up registration more broadly."
https://support.bittrex.com/hc/en-us/articles/115003463331Posted Dec 2017!