Cancellation of the cellphone contract.

I have or rather say had a cellphone contract with Telkom which ended 31st of October 2017. I called in Customer Service Centre on the 23rd of October to verify that it is my last installment and spoke with Katlego Sefularo, she advised me that i should fill a cancellation form which she sent to me, I filled it and sent it to their Cancellations Department. I called a week later to find out if they received the form but I was informed by a call center agent that the requests have a turn-around time of 21 days and I was advised that a person cannot even call the Cancellations Dept because they don't have a direct line (I was very disappointed at that statement as Telkom has been around for many years not to have contact number for their Dept). And now, a week ago on the 4th of November, I received a billing invoice for November of which I am not suppose to be receiving as I sent my cancellation form.