Luggage damaged on purpose

I checked in my luggage on Saturday for a flight from Durban to Johannesburg. I had secured the bag with a lock. However upon arriving home i noticed the lock was only on one zipper tab. I noticed the other tab was completely broken. When I opened my bag my clothes were a mess someone had definitely been in my bag and my cosmetic bag was open. I am now unable to lock my bag as the tab is broken and it's a fairly costly bag. When I contacted Flysafair the response i received was that they are not responsible for wear and tear. This is not wear and tear it's damage done purposefully. If they needed access why couldnt they call me.I am completely and utterly disgusted at the response I received. My bag was locked, I feel so wronged and violated right now.