Incorrect subscription billed on my account

For the Past 3 months I have been getting charges on my MTN account that are 3rd party charges. I have phoned their Cape Town number for them to unsubscribe me from this mydownlow. The question is how can I be subscribed to a service when I use a modem on this number. How so? Their support team can only reply in writing but when they deduct money they don't do it in writing. As a consumer I am very much disappointed from these companies that suck the blood of the innocent.