MTN Failed me again

I've been with this network for years. Have an active contract with them which I pay monthly via EFT. I've recently received an email that I owe MTN 236 and they will I will be blacklisted if I don't make the payment. This just before I made yet another payment. I called to enquire but didn't get any clarity. I asked what can I do to get the outstanding amount so I can settle and cancel my contract. I was transferred to retention dept. There I was put on hold for almost 30 minutes with no assistance. I had to drop that call as I had somewhere to go. MTN failed me, once again☹️