Not sure how the hacker has done it without

1) 2FA being enabled on your account
2) Email verification on yobit's side
3) Login notification not being sent to your email

The only explanation i can think of is that all of your accounts have been compromised, your email, google authenticator, etc. Or it was one of your family members doing it that has physical access to your computer and mobile phone.

Just a heads up though, in these scenarios yobit can't do anything. Even if you contact support they won't be able to resolve the issue, the only trail the hacker has left is the yobicode. You may be able to ask the support to verify which account redeemed the yobicodes(even though it's probably a throaway).