MTN insurance pathetic

I seriously do not know what to do anymore. I have all my devices on MTN insurance. The one device fell and the screen broke, and was sent for repairs. After i recieved the device back, it was freezing the whole time and then we have to wait for it to go completely flat and charge it before it works again. We sent the device back, and it was returned with the same problems. The phone would just start doing its own thing, screen jumping around etc. The 4th time it went back they said the memory is full thats why it was doing this. I did not buy this, as it wasnt just slow like when the memory is full. They returned the device and we cleared the memory. Same problems.I took Seperate videos of where the phone froze completely and where the phone just goes haywire. It went back for a 5th time. I told them that I want a new phone as effectively I have been without a phone for months, paying my insurance every month. They just sent back a email saying nothing is wrong with the phone and they are sending it back. This while I have video prooof of the phone being faulty. I have tried everything trying to get them to replace the phone. It does not work and they cant find the problem. I don't know what to do