Put a small hidden video camera inside of an object. Preferably a small trail can that can be hidden inside of an object. It will take snapshots of the person who opens the safety deposit box. Check on it every couple of weeks to see who has been rummaging around.

Then you have hard photographic evidence of safety deposit box tampering. Violating the customer relationship agreement. That can be utilized in a lawsuit by a skilled lawyer. Which can be in return used to seek compensation in Bitcoin.