Consumer protection????

I have a huge complaint with MTN and we need a contact number where we can take this matter further?? My husband bought a CAT S60 at your MTN branch in Cape Road Port Elizabeth. The phone is only a year old. The touch screen started becoming faulty so he went into MTN to get it repaired. They took the phone and sent it to JHB MTN repair center. After waiting two weeks, he received an sms saying he must pay an amount of R4000.00 for the damages. With a connection in the JHB repair center we were able to find out that the reason they are charging us was due to MTN not giving them a proof of purchase. He then went back to MTN in Port Elizabeth and advised my husband that they did send a proof of purchase and that they would resend it. After another week, we checked with our connection and they still had not received proof. Only after everything, my husband goes back to them and gets told the phone is now on its way back to PE from JHB as MTN can't do anything with the phone, it is beyond the repairs that they can do. My husband will have to get in touch with CAT directly and they must fix the phone!!! Now I want an explanation as to why should the customer sort out this issue with CAT as we got the phone through MTN?? And I want to know, if they can send a quote then why can't they repair it?? Giving us a quote means they know what's wrong with the phone and are going to fix it. I want answers! Someone who we can talk to that can give us proper answers?? Thanks.