Fix my billing MTN, I don't owe you!!!

In March 2025, I called MTN to cancel my cellphone contract. Their Retentions department convinced me to take a cheaper option, to which I obliged and paid the early cancellation amount, which was for the device that they told me I needed to pay for. However, since the new contract started, MTN has been billing way more than what I was even paying before and when you call them, no one seems to be able to help, I've been sent from customer service, to billing, to retention to collection, and then to billing and retention again. One "service loser", Ayanda at Collections, even cut me off before I could explain what the issue was and sent me back to the queue. And then they have the gall to suspend my calls.