Upgrade misery/Poor Poor Service

I did my phone upgrade with the retentions department (they called me to remind me that I was due) in November 2019. I received my phone on the 29th of November. The phone had a speaker problem and I had to use loud speaker for some of the calls. I sent an email to the lady who assisted me with the the upgrade to ask what I needed to do to return the phone, no response. I called the retentions department and was told to take it to an MTN store. When returning the phone I found out it could only be returned to an MTN direct store (which was news to me as I was not aware they were different) which I did in East Rand Mall on the 5th December 2019. I was given 3 different numbers to call, 1 for the store to confirm the phone was collected. 2 for the warehouse to confirm they received the phone and the retentions department once I received the reference number from the warehouse. I thought it was strange that I should be calling their warehouse after having given them the phone. I ha ve been calling the retentions department explaining this story from one person to the next not to mention the holding on which can be about 20 minutes. They kept telling me they are waiting for the reference number from the warehouse. What I fail to understand is that how is that my problem that their warehouse is not giving them the reference when I gave in the phone at their store. They have not called me back once but every time I call someone promises to call back. This is the most bull **** service I have have received considering how long I have been their client. The worst is that nobody seems to care I must keep calling them for feedback and still nothing. Month end is approaching and I will be billed for a phone I don't have and they tell I can be reimbursed. I wonder how when they can't even find a phone in their system. I just want to have the damn contract canceled.