Unfair treatment

I write this complaint for the unfair treatment I am receiving under my MTN contract with you. I was contacted in march by a call centre agent who offered me an upgrade. After telling him that my upgrade was only due in October, he told me that it's only due in October if I upgrade in store, but because he is calling me I can upgrade then. i accepted the upgrade only to be given a bill for early upgrade.I called in to dispute to dispute the early upgrade fees and was told they would listen to the call and determine if my dispute was valid. They contacted me to say that my dispute is valid and would pay me for the early upgrade fees within 2 weeks. After over 3 weeks had passed I called back to enquire as to why the money had not been given to me, I was then told that payment is declined and i must return my old device. I refused this and indicated that whenever i do an upgrade i do not hand my device back and i should not be doing so in this case just because the agent made an error it should not leave me worse off.I was then told that i have two options to return old device or new device and cancel contract. I opted to return the new device and cancel the contract. I called the call centre again to this effect and they wrote email attached and indicated that they will pay for all costs related to cancellation. It has been a week and i have not had any feedback. I am being billed for a device I do not have and also have arrears for an early upgrade I did not do. My credit score is obviously being affected and i demand that this be resolved urgently without me being in a worse off position than i was before the call made in error by your agent to me and upgrading me in error