MTN and Woolworths Cresta

I am the owner of a broken cell phone Hisense F22 that I purchesed at Woolworths Cresta on the 23/03/2018 . I have recently been overseas for 3 Months I took the F22 phone with me ,the phone worked for 1.5 weeks and then would not read the sim card anymore as I did not have a working phone I had to buy a new smartphone overseas at my expense.On return to South Africa I took the phone back to Woolworths . The assistant and store manager would not replace the phone ( 5 Months old and only worked for 3 months) and told me that the phone had to be sent in to MTN for repairs Doc No ********** dated 28/8/2018 .I still do not have the phone back. I have been in contact on the phone to Woolworths on numerous ocasions and have been given the run around so I decided to phone MTN direct. I spoke to someone there and he assured me that they have the phone and is ready and will dispatch repaired phone back to Woolworths Cresta that same day that was 2 weeks ago. Still no phone. My problem is that I feel that I do not want a Repaired phone after 3 Months of actual use ) . I feel as customer service MTN should furnish me with a new phone and transfer all my info for free although that could take another few weeks?. Please Help as I am at wits end with Woolworths and MTN.