Billing ****

I am really not happy about the service I am getting first it was a hassle to return the faulty phone I was given on contract I hardly used the phone (2015). Eventually, the phone was collected and no replacement was done. It was a mission to try to get through to them as I was being put to a lot of people who seemed like subcontractors. I gave up on this as I was wasting a lot of airtime trying to resolve this. Boom 7 years later I pick up I am owing an amount of R953.00 as I was trying to apply for something, How do I even pay for what I have never used?