Cancelling of MTN Wifi Contract

I’m really disappointed with how MTN has handled my situation. After emigrating, I followed all the necessary steps to cancel my Wifi contract, giving a month's notice and returning the router at the MTN One store at OR Tambo Airport. Despite this, I’m still being charged monthly. When I reached out to customer care, I felt brushed off since they said they couldn’t help me because the contract was online. I was given an email to contact but haven’t received any response since I reached out in November. It's frustrating to be in this position, and it feels like MTN doesn't care about their customers. I'm not sure what to do next.