NBA Settled Account - Harassment

In November 2014 we received a letter from Nashua Mobile that our contract is being moved to Vodacom. So as from the following month, we received a vodacom account, which we paid ever since. Now 3 years later the above mentioned attorneys is phoning us about a contract that we have with Nashua Mobile and we are liable for payments to them. We have tried to explain and also sent all documentation to prove our payments. They now have become an harassment, as they phone everyday and say that they will keep doing this adding a daily R20 fee for the call. We do not know which way to turn now, Please could you help. We are quite prepared to send you any documentation required. Our reference number with the above attorneys is : 1NSH007242, Mr Quintino Gouveia. ********** 617.