WONT REFUND ME MY OWN MONEY BACK

I have two contracts with Vodacom, up until recently i found out that i have been over paying into my vodacom account, I had contacted customer care and have been given the run around for three weeks now....im highly annoyed everytime i call they either cut the call or have no valid answer for me....i received and sms this morning to state that i should provide proof of payment for them to do a refund, however it clearly shows on their own statement that i have been over paying in CASH might i add.....so now they want me to go to the bank where i did the deposits and get proof from the bank yet i say again it clearly shows that i have been over paying....for three weeks now i had to deal with people that seem to know nothing....is it that hard to refund me my own money back...really upset customer