Dissapointing service

After purchasing a faulty laptop, I reported the issue at a Greenacres branch and was instructed to report it online for collection. However, communication was poor, and I was transferred between consultants. Despite being promised that the laptop would be collected for repair, I waited over two weeks with no response. I attempted to communicate with them numerous times after that and I received no reply both from customer service department and from the complaints department. After paying for a laptop I couldn't use for more 6 month till to date.I decided to stop their debits. Now, they have listed me as a bad payer, negatively impacting my credit record. I am frustrated by their service and the detrimental effect on my credit.How do I resolve this? This is the first time I am having issues with them, been with Cell C for over almost a decade now. This treatment is really disappointing.