Frustrated by MTN

Hello Peter I bought a Sumsung S9+ at MTN Store in Hemmingway's mall East London. This is the phone they have just released in February 2018. I got this phone on the 23 March 2018. In June I started to experience battery problem meaning the battery couldn't last even 4 hours. I took it back for them to fix. It was such an inconvenience because I lost every information that was there. It came back ,battery problem was sorted. Later I noticed that the device was deleting some of my messages without me deleting them including pictures and whatsup. I am running a business and need these messages that can one day becomemy evidence. I thought maybe it was just gonna stop but it became worse. I took the device back to MTN store again, they fiddle with the device and advice that probably it was the settings or a software that needed to be updated. They told me that all was well. Two days later I noticed that the problem was still there and decided to go there again. They advised me to go to D&D which deals with Samsung phones in Vincent as they can not figure out the problem. D&D quoted me R250.00 for fixing the problem. My phone is still under warranty for me to be paying other amounts. I rejected the quote. Back to MTN, my device is now booked in for the second time and I have been in and out of their store. I have explained my situation to the Manager that this back and forth need to come to an end I demanded to have a loan phone in the meantime which they gave it to me though it doesn't solve the problem. I demanded that I must be given a new phone, they told me that my earphones were not in the box and therefore my device cannot be replaced but fixed. My question to them was that what was it that they were going to fix that they couldn't fix before. They have wasted my time, I lost information in the process now I'm throwing my money on the drain for something that is not working properly. The manager Sifikile -her name ********** , doesn't bother at all. I requested that she view the camera so that they can see that the earphones were in the box and she told me that the camera info only last for few days and it gets deleted. This phone is more than R20 000.00 for them to be treating me like this. I am very frustrated. Peter please help me. Tembi Mphafa