Over Charged & demanding payment

I have 2 VC contracts on 1 account. Revieved an SMS saying i owe money and have defaulted on payment. When i know my 2 contracts are fixed monthly fees every month and having been paying via EFT every month the same amount. So i call in to find out whats going on. As its embarrassing that i received these messages, as someone else is using the phone, of which i am paying for. This bill is paid every month on time with out fail. Its not my fault that you have a ****ty billing system or your accounts department cant pick up payments in advance. I have been a long standing customer of Vodacom and right not im not a happy customer and will be spreading the word fast about the bad billing service.

I demanding this be rectified. I trust this does not affect my ITC report and ensure that i have not been marked as a bad payer. I await your response.