Cell phone billing

I open the cell phone contract with Telkom in 2015 for capped amount R159.00 per month till 2017 Nov when i upgraded the cell phone and the amount went up to R264.49. Everything went smooth until 31 May 18 when the debit order of R751.32 went off my account. I did enquire with them on the 01 June 18, when the consultant advised me that the agent at Fourways Telkom store was supposed to activate the monthly debit order to be capped to R264.49 and he did not do that. On 22 May, after numerous phone calls without any joy, feedback was "it was my responsibility to check my account and not use out of capped amount, so they will fix everything but they will not reverse the money". Again on the 30 Jun, another amount of R607.18 was debited, when i required again, they said they debit the correct amount. According to the contract that i signed with them, only the amount R264.49 should be debit and the was confirmed immediately after the first big amount was debited. Now i get penalized for Telkom's employees who are not doing their job properly. This is the company that i have been loyal for almost 3 years without skipping any payment and they are too quick to pass the blame back to me and fail to take responsibility.