Incorrectly billed

I am so annoyed by the terrible service I am receiving from Telkom mobile. I have been incorrectly billed for someone's else's data bill and a month and a half later I have yet to receive my money back! My first question is how can my bank details incorrectly be added to somebody else? Is there not a law or something that protects customers against this type of thing? How was my details verified for somebody else. I was also receiving this person's invoice to my email address I might add... I called to let them know the very day it happened and told them the full story. And that they must pls sort it out so that it doesn't happen again. I have spoken to about 20 diff agents in the process. And guess what? It happened again the following month! Absolutely ridiculous! I had to go to my bank who was then able to reverse the last amount. But the first amount they were not able to. I then get an sms saying that my case is resolved expecting to hear that my money will be back in my account in a few days and they say no they have given me a credit! when pre tell did u ever say that I want a credit!!! I want my money back. And guess what its now another week later and I haven't heard from anybody. Can anybody help?