********** agents and bad customer experience

After years of excellent service with Cell C they finally did me dirty and have not stopped. One of their agents tried to upgrade my expired contract and I refused. A few weeks later I got a call claiming that I had taken out a new device, only to find out that it was their own agent who took it for themselves with my details. My bills were messed up and I was reversing debit orders for months. When they finally decided to cancel the ********** account they then messed up my billing and I am now required to pay for the services that I have not used, I was told by an agent that I had not paid my bills in 5 months. I emailed her my bank statement and she never rep****. But I keep getting calls from collections to pay up when I'm supposed to be getting follow-up calls. This is ruining my credit report and I am tired of calling agents who don't care about your enquiry, I've had multiple agents hang up on me whilst trying to explain, sometimes they say the back office will call but nothing happens.