Vodacom billing kills my credit score

I checked my credit rating and discovered it has been downgraded because of outstanding bills from Vodacom. Meanwhile I have paid and have a proof of payment. Despite sending the bill to my email address, not once did they email me any query. Instead they have been phoning my mother! I told her to tell them I have paid. Clearly they did not listen. This will probably effect my ability to get a home loan now. Unbelievably *********** and malevolent even.