Still receiving SMS to pay for mobile.

During the week of September i took my phone in only to get a software update in which MTN came back saying i need to pay for other repairs and shall i not, i shall be held liable to pay a quotation fee. This was not brought up when i took the phone in as the phone is still under warranty. I refused to pay the amount to fix a phone for repairs i did not ask for or need. The phone was working perfectly fine until a software update failed. I have called in and came to the resolution that i will not be taking the phone back unfixed. I thought i made it clear that mtn may now keep the device as I will not pay for a device that is returned not working. I still get SMS asking me to make payments and for the last time, i WILL NOT make payment for a phone that is still under warranty and that I was not notified about when I took the phone in. <br> This is really disappointing behavior from such a huge company as even your retentions department could not come to a resolution when I told them why I wanted to cancel my contract yet you say you will do anything to keep customers. The smallest network in SA has much better service than this. Job card no. MSCGU***. IMEI: ***