Since 2016 I had a Data contract with Cell C

Since 2016 I had a Data contract with Cell C. It was 24 months contract and if the contract expire i will get an offer for new deal. I completed my contract this year May 2023. I never got payed up letter or notifications or either an offer. I was surprised to find out Cell C stating i owe them while i never got an offer or payed up letter or service to the router in which the Data was served. They have attitude towards customers who are not interested with the service, they ignore the request made by client for cancellation procedure. Please note they use lawyers to accept that you owe them while the reality is not.