Lack of integrity from Telkom

I am very much disappointed by the lack of integrity by Telkom. I took out a cellphone contract in March 2018 with Telkom. Everything was fine and the service I received from Tawanda in Fourways mall was awesome. She explained everything clearly. She asked me how much I wanted my spend limit to be and I advised her that I wanted it to be R0, she recommended that I make it R5 of which I did not object. Everything is been fine up until end of October 2018. For the month of October an amount of R899 was debited from account which I quickly reversed because I knew my monthly contract amount is R374. Upon checking my previous month's statement I leant that the R899 was the amount to be debited. I went to the nearest Telkom store top find out why my bill was so much. I was told that I had spend R500 on my spend limit, I told them that my monthly spend limit is R5 and after they checked I was told it is on R500. When I asked who increased my limit, I was not given answers, instead they reduced it. This is unacceptable from Telkom. I am not prepared to pay that amount because this is Telkom's fault. They increased my limit without my consent. I am willing to pay my regular subscription fee.