Unknown charge on my account and horrible customer service.

I had an mtn month2month home router and paid the overdue amount last month. I was assured that I do not owe anything after settling the payment. Same day I received an sms saying "urgent reminder to pay R2498.50 or your services will be suspended. Mind you I haven't had services for months as the router was disconnected. I went instore and the consultant couldn't explain what the charge was for and advised me to call customer care. I called and the agent also did not know what the charge was for. She said she'll log a dispute and gave me a reference number. I did not receive feedback so I decided to call again this morning. Billing agent was not able to assist and put me through to collections. The collections agent was so rude and hung up on me. I am so disappointed by mtn and I will be taking this further. Mtn agents don't seem to know what they're doing.