Cannot get their billing right

Vodacom just does not seem to get their billing right. Got a call a few months ago informing us we were behind on our account which surprised me as I have had the same account to about 20 years. Eventually after being pushed from pillar to post it was sorted. Once again yesterday I get a call again we are again in arrears even through I pay every month the amount agreed upon during my last conversation. Really Vodacom get it right. One more thing when a representative phones and cannot get hold of me how about leaving a phone number I can phone you back on as sometimes people are not available when you phone so just leaving a message with the fact you phoned helps no one