Billing broken somehow

I've had unbroken billing with MTN for all of my contract and in the last month their payments haven't gone through. They charge on my credit card, which always gets zeroed every month and is never (ever) near the limit. Today I was just cut off with a demand to pay. MTN, if you're cutting me off it's because you and the bank have some glitch that has nothing to do with me. Charge my card and get on with it! Or send me an actual issue report so I know what to do. Or contact the bank to see if there's a reason. I sign the agreement and use the phone, you and the bank are the experts at processing the payments. Why make it my problem?