Settled account and rejected insurance claim

I have a very bad review for MTN I am really not happy with the service I got from them since October 2023, I settled and closed my contract in October and around November/December I received a paid letter from them saying that my account is settled and closed, just 2 weeks ago they send me a statement saying that I owe them R2000+ which I am failing to understand where is it coming from because I don't even use their sim cards anymore it has been 4 months now, my credit profile says I have MTN account in default, how so???? Secondly I had a cellphone insurance with them my phone was ******, I claimed insurance and it was declined their reasoning is that I was not using their sim card when the device was ******, do we insure devices or sim cards?? MTN your service is veryyyyyyyyyy pooooor starting from your stores to call center.