Breach of Contract

Almost 2 years ago i have signed for a R299 a month WiFi contract, all has been going well until on the 01st May,they decided to deduct R799 on my account. When I phoned wanting clarity & rectification, I was told that i was charged for the additional data that I have used. Mind you my data was already finished & switched off around the 23rd April. When I told the consultant that every time my data is finished, Telkom usually cuts it until the next month, which is what I signed for & it was the case this month.- she insisted that I had an allowance to increase my limit with an additional R500, I asked her to check my account for usage and analysis as I have never increased my limit & have never app**** or used additional data - she flatly refused to assist me. Had I wanted an uncapped Service, I could have app**** for it mos. How do you justify inflating my agreed account with almost 200% something I never agreed to especially for a service that you have never provided to me. This is unacceptable & a gross breach of our contract /agreement. I never agreed to this nor even received nor app**** for additional data - I hope someone would respond to this as the consultant was arrogantly denying to resolve my issue