POOR SERVICE FROM VODACOM

Vodacom has incorrectly listed me as having a payment history resulting a a lower credit score. I have contacted Vodacom legal department and they have admitted that they have made a mistake and will rectify with the credit bureau. This is however affecting my ability to obtain vehicle finance. Now they do not answer my calls and are not responding to my emails. How can such a huge financial services provider have personnel who make mistakes that affect the day to day operations of their customers but are not proactive in resolving the matter. Please assist.