****ed off customer

I've been calling mtn from the 6th of September regarding my contract I've emailed customer service and supervisors nobody has returned my emails or call last month they have double debited my account went to mtn store in midway mall uptill today nobody's has contacted me I've sent a letter of cancelation but still they are debiting my account I don't know who to speak to cos the service they provide is not what they advertise I've been a customer for more than 4 years but still receiving **** service and I have proof of emails sent to customer service