Appalling Service

I ordered an iPhone 13 online and I took delivery of the phone on Tuesday the 19th of October. The phone was faulty and was returned through MTN Morningside on Friday 22 October. I have been calling Mondo continuously, in the beginning every day, then down to once a week since October to try and get this contract cancelled. Now we are already at the end of January the contract still has not been cancelled. Each time I call Mondo I speak to an agent who tells me the cancellation has been escalated as they have an RMA number and the phone was returned to the warehouse. I am still receiving monthly invoices from MTN and run the risk of getting my credit ruined over this.. This is really terrible service as surely it should not take this long to cancel a contract for a phone that was returned within two days. The time and airtime wasted on this is just ridiculous.