MTN Service = POOR

Every month my phone service are being cut, and every time the service consultants cannot tell me why! As I don't receive invoices monthly (I reported this every time I talk to someone, but still nothing is happening) I pay what I originally agreed as a fixed monthly fee. Last week I was told that I owe R55, which I immediately paid, and my phone service was restored. This morning the service was suspended again, when I phoned, and after waiting for 15min to be helped, I was firstly told I owe R200, and then later R500+ by the consultant!! What is going on MTN!!! Your systems are definitely not functioning the way it should