Customer vs MTN

If there was a zero rating I was going to choose it. I received a router and it wasn’t working. Reported it and returned it to the shop within 7 days. Even that was a hassle. Mtn kept on deducting money from my account even though I’ve never used their services. An amount of over R1000 is owed to me. I have been in multiple calls with mtn and they say they can only refund me R500. Fighting for what is mine is emotionally draining. Even with that I am being told that they need proof of which I have sent, multiple times and I am being hit with “we have not received anyyhing”. This is going on 2 years now