Of course there is always a possibility that within an exchange there are immoral actors that are abusing their powers, however I don't think that you have sufficient proof that it's something that was done by the inside. Even if it was, you simply can't accuse them of doing something wrong when you don't have the proof.

If the hacker actually had access to your email, then it would make sense since he could have simply deleted all of your emails. The chances of someone hacking you compared to yobit targeting you individually are probably much higher, even though they are very shady.

Change all your passwords straightaway, including your email. And yes, stop using yobit. Yobit is one of the worst exchanges that have ever existed.