Paid for repairs that never happened

I sent my son's tablet in for repair. They assessed it and said they could fix it. They charged me R1100. When we got the tablet back, it was not charging properly, so I took it in again for them to fix. They kept it for 2 weeks! When I called to find out what was happening, they told me they were waiting for parts. The next day I came to collect it and the lady behind the counter told me that they never did anything because it was charging and they just gave me a new charger. When we got home - guess what? It's still not charging. Now they won't answer my calls.