Bad service

I am so disappointed in MTN,I took a contract a year ago and they have been debiting without any issue,last month I received an email saying that I missed my payment and I was shocked because MTN debits from my account according to the agreement but it appears that they didn't this time and wanted to make it my fault. I checked my account balance and there was enough money in there but still,now they closed my SIM so that I don't make calls, and sent email advising that I should go to the nearest MTN shop to sort this out, question is that why should I be the one running around whereas all this is not my fault,is this a good service? I believe MTN didn't stick to the agreement as per contract but now wants me to clean mess,money is in the account,they didn't debit and now I'm the one to fix this? Nah.