With the current AI technology, someone can use your face and your voice, which will make the wallet won't able to verify if it was you or it was a fake person that pretends to be you.
It could be the exchange employees has stolen the btc and blame to an external hackers.
then still you can get it back but you need to file a criminal case to the police. The Bitcoin Police will provide you the KYC code for your Stollen BTC then the police in your country can find out the stollen btc for you and return to you.
Look, if you can think exchange employees can steal your coins, there's no difference with police because they can steal your coins too and blame the other people. If you can't trust someone, it means you can't trust anyone.