Billed for data on a sim card that is not in use

I am utterly disgusted with the service received from Vodacom customer care. On the 28th of February I was debited R1899.92. To my shock I went to the Chatsworth branch and queried as to why I was billed this when I have not been using this sim card since 2014. I was told that they would not be able to assist me and that I should go to the Gateway customer walk in center for assistance. The following day I had done so and was told that there was no reason why the Chatsworth branch could not help me as they have the same system that Gateway has, and that the billing seems to be in error and that this sim card is indeed not in use and that there is no way data could have been purchased. The consultant then issued me with a service request number S3-8Z12W-W8IFU and advised me that I should phone customer care after 3 days and find out the status of the investigation. After a few days I called and was told it is still under investigation. On my next call I was told a credit of R700 +/- was showing on my account. So I asked them why only this amount when my credit should be R1461.42? to date i have not received one phone call from Vodacom neither have i received my credit.