Customer service. WHAT customer service?????!!!!!

I currently have 2 cell phone contracts with MTN and have been a customer for 20 years. I upgraded in December 2017 and was astonished to have a call cut over a weekend about a month ago due to having reached my "credit limit". When I called MTN to enquire I was told that my limit was set at Zero (who told them to do that no one knows!), but that she could reset it for me at R440. When I enquired about this small limit I was told this is the allowed amount as per the credit control department. I then asked to speak to someone in the credit control department and was told someone would call me. This NEVER happened, instead I got an sms telling me my query has been resolved - IT HASN'T. I called again last week and was told again that it would be escalated to the credit control department who would contact me - AGAIN THIS DIDN'T HAPPEN! Instead I got another sms telling me my query has been resolved. I called again today and was given the same nonsense. I was also then told that one can only increase one's credit limit every 3 months, so I would have to wait until November!!!! I did not ask for a credit limit on my account, nor did you discuss imposing this ridiculous limit - I do not need one, I can afford to pay my account many times over, and I have NOT in 20 years defaulted on my account even once!!! Yet, you have the audacity to treat me like this!!! Is this what you call customer service?????