Frustrated Customer of MTN

Most Frustration to deal with - My contract reached it's expiry period and I cancelled it, despite writing e-mails and making calls, I am still receiving invoices. My e-mail got referred to the retention department, still no communication from them, but I received an e-mail advising me of the rate change. When enquiring about the invoice I was told that it was an early cancellation fee, I did not cancel my contract early, still waiting to hear what is going on with my account and I am also afraid that due to no payment being made to an invoice I do not think I am responsible for MTN may blacklist my name as it seems that nobody knows what they doing at MTN.