Mtn and Mondo worse cellular company

Mtn rewards calls with a deal do not accept it. Mondo and MTN gives the worse service. They can not resolves their problems just says it's escalated. In March 2021 I entered into and agreement with a router which was a deal. In April the router stopped working. I took it to the Mtn store on 22 May 2021. I was told that the router is faulty and because It was under the warranty. I can either have it replaced or cancel the contract. I opted for the latter as by this time I was going in to the store for answers. No one ever contacted me to inform me. Cancelation was not processed until October. I was being billed for an item not in my possession. Mondo has emailed me in November to inform that they have escalated for me to be credited. Yet MTN says I am in arrears. Jameelah