Lost my bag and making it my responsibility

I flew back home tonight on SAFAIR, when boarding in JHB they took my hand luggage to put in the hull as the plane was full. Upon arrival when I went to pick up my bag I realised it was not there. Upon enquiring I was informed that someone else must have taken it and I will just have to wait until it is returned. I asked them to open the bag that was left (which looked similarly to mine) to see if they can find details of the person so they can be contacted, they did open the bag and after looking for a full 5 seconds told me that there is nothing but clothes inside. I spoke to the supervisor who also told me that they will contact me if and when my bag is returned and I will then have to come back to the airport to pick it up. I left my bag in their care yet they are now telling me it is not their responsibility to ensure that I get my bag it is personal luggage and it is the passenger’s responsibility to ensure they take the correct bag. Not sure why they even tag the bags and give u a stump as proof if the bags are just outside the plane as a free for all and no one is monitoring that firstly you even have proof that you handed in a bag and secondly that the stump matches the tag and then wanting to hold you responsible if your bag is taken. Not even attempting to find it or offering to get it to you once it is found. The worst service I have experienced in a long long time.