MTN South Africa Administration and cancellation process GAPS

I was relocated to work abroad in 2018 and January 2019 I flew back to South Africa to manage all administrative-related matters, one of which was to cancel my MTN mobile phone account, which I cannot use outside of South Africa.

In the MTN store, the lady said that I must phone a number to cancel the call. While still in the store I phoned the number and gave all details for my account to be closed. The MTN lady on the phone confirmed that the account is closed. I then also paid the full remainder of the contract to effectively have it closed. The MTN lady behind the counter in the MTN store whom I paid the amount to, also confirmed that my account is closed and that it will be seen in 24 hours.

Since then, I have received electronic accounts each month to show that my account has a positive figure, which is INCORRECT as I should NOT have an account with MTN any more. I consequently sent an email to MTN's customer services explaining all - NO feedback. Today (end March 2019) I receive an account statement again. I phone to South Africa, explain the whole situation to the person on the line, but the person cannot assist me today (Wednesday), I must try again on Friday (?!) - no reference number, should just dial 135.

It is extremely unprofessional and unrealiable and this whole process is costing me a fortune. PLEASE MTN, can you just manage the STANDARD ADMINISTRATION you put in place and cancel the contract, because your stipulated process was followed to the T.

Really hope to receive feedback soonest possible.