Why do you do this to loyal customers?

I have never been so disgusted in the type of service MTN provides. First of all, I signed up for a Top-Up contract (THIS USUALLY MEANS THAT WHEN YOUR MINUTES ARE DEPLETED, YOU HAVE TO TOP-UP WITH MORE AIRTIME...). I checked my statement this month, and it has doubled? When I queried it, the consultant on the other line told me that when I do not top-up myself, MTN will automatically top up for me? Now, I have NEVER signed up or agreed to any of this on my signed contract? I have been a customer for more than 18 years, and I am so EXCITED to cancel my contract with MTN! The number the consultant provided to speak to the cancellations department is *** / *** - non of these numbers work, so how do I cancel with you? Why do you do this to loyal customers?