Very Poor Service: VODACOM

I have had the same Vodacom mobile number for +15yrs and payment has always been done via c/card. My c/card details have changed and I cannot get Vodacom to change my details.!! For two month’s now Vodacom has sent me messages that my debit order has been rejected. It is rejected because the details on the card has changed (expiry date!) it is impossible to get Vodacom to understand this simple matter! I have spoken to 6 idiots today and not one can help me