Returned router but still need to pay for it

8 June 2021 they brought me a home router instead of pocket router I then returned as instructed it was within 3 days of delivery. I phoned to make a follow up but it took months to be cancelled yet I was billed for that. I took a pocket router immediately after that because I needed a wifi but the problem was that my account was linked with the one I returned and I had to stop the debit order till they sort my account which they promised to do and my pocket router services were stopped in August but till today I get an email which state that I am owing close to R6000. I phoned and went to the branch in pmb Midlands mall for this matter to be resolved but they couldn't help me. How can my name be handed to Mtn legal as i did everything to be assisted in order to pay for my pocket router which I insisted for it bring separated from the home router that I did not use. Ms LP Makhathini ***