MTN contract cancellation struggle for more than 3 months

I canceled a new contract on the same day it was delivered(13 February 2023). I wanted to do it beforehand but the retentions department consultant advised it wasn't possible as the device wasn't yet active. The device was picked up by the MTN courier company again 2 days after it was delivered. After more than 3 months I am still struggling to cancel the contract. Nobody at the call centre knows whose responsibility it is, on numerous occasions I was transferred to the device repair centre and they refuse to help as well.