Suspend my line after payment was made.

I received my monthly bill as usual. Did payment on the 27th of May. The very same day my line got suspended. Phoned the call centre and they say my account is in arrears. The statement sent through did not show any arrears and the account is up to date. They blocked my line because payment was not made by the 26th. I would like to know how they can suspend my line before the 1st of the following month. If I receive my salary on the 25th. Once it reflects in my account I can make payment to cell c. Will they be blocking my line every month now? If Vodacom or MTN offered contract buy out I would be the FIRST to leave Cell C.