I got a scare like that about a week ago. A week before everything was fine, but then Bittrex said my withdrawal limit is 0 BTC until I verify my account. Public info verification failed for some reason, so I had to do the extended verification but thankfully in my case that process only took half an hour or so and I could withdraw my money again.

Of course then I figured out Bittrex charges a 0.001 Bitcoin tx fee for withdrawals, which is $18 right now, so I just exchanged everything for Dash, sent it to another exchange and withdrew the Bitcoins there.

But yeah, be careful with exchanges in general, never store money on there, just do your transaction and get out. My father bought his first 1.2 Bitcoin on Bitcoin24 which was the biggest European exchange at the time I believe. That's worth $23k right now. 2 weeks later, they stopped withdrawals and the exchange shut down. I've had to call their lawyer again and again and he always promised me they'd send the money soon but they never did and then they apparently fired the lawyer so I couldn't even contact them anymore. My father has hated crypto currencies ever since and gets mad if anyone as much as mentions Bitcoin, especially seeing how much it is worth right now and since he could really use the money.