Telkom billing

I received my monthly bill for July and I was billed for extra data R400 when I have enough data to use. I went into a Telkom store and they could not help at all, pushing me from pillar to post. They asked me to contact their customer service department and they were not helpful at all. I wrote an email to their service department manager, with no response to date. Thye guys in the Telkom store said that my data roaming is on, I showed them the phone physically that it is off as I never use data roaming. To date, I can get no help to resolve this problem. Telkom provides poor useless service, I have about 4 contacts with them and eventually will be canceling them on expiry.