Overcharging and Poor Customer Service

I had taken out a SmartBroadband Wireless10GB contract with Telkom at the beginning of 2018. For the past few months I have been debited with a fixed amount of R 365.10. In November 2019, I received an invoice advising to pay an amount of R 3,915.84. I then called Telkom call centre to find out why I am I being charged this amount. The consultant that had assisted me had advised me that I had gone over my limit and that’s the reason for the amount provided. A few days later, when I tried to connect to my WIFI, I was unable to do so as it advised me that I am out of Data. I am not sure how I went over the limit as it would generally cut off once I reached my limit and I did not call Telkom to increase the limit since I’ve had the router. I have tried numerous times to contact Telkom regarding the issue but till date have received no assistance. I refuse to pay the amounts which they keep debiting me for as I want a reason for the ridiculous increase that I was not aware of.