Shocking service and not able to produce proof of purchase for my contract

I have a Samsung s6 edge on contract with MTN. Unfortunately I cracked my screen and wanted to take advantage of the free screen replacement offered by Samsung. Samsung requested a proof of payment which I unfortunately did not have. This is where the trouble started. I tried to get a proof of payment from MTN, however they were not able to assist me. I went through to different stores and finally contacted MTN on social Media. After this, I received an email from a lady by the name of Kubera. She provided me with a document, which does not resemble a proof of payment. This was in November 2017. I checked the document and it did not have an IMEI number on it and the serial number did not match the serial number on my phone. I mentioned it to her, but she insisted this was the absolute only document available and that it did not matter, samsung would accept it and repair my screen. I was hesitant but took my phone to the repair centre in Canal walk in January 2018. They took my phone and I heard nothing from them. Eventually I got hold of them in early April and they advised me the proof of purchase was not sufficient and did not match my phone details. Exactly what I had pointed out. I still do not have a phone and have contacted Kubera 3 times with no response from her. This is shocking service by both MTN and Sumsung. However, I am confident that according to the consumer protection act, mtn is legally required to produce my paperwork and ensure that it is correct. I mean I am billed every month for a contract, surely they can produce a proof of payment. I have requested to get my phone back from Samsung and have also not heard back from them. I insist that MTN replaces my screen at no cost to me to compensate for their lack in customer service, communication and not being able to provide me with the correct paperwork.