Telkom Incorrect Billing

I have a router at Telkom and I pay R369 every month, for the month of July I was charged R1489 for out of bundle rates. I do not understand how as I always call increase my spending limit so I can buy additional data if required. I went back and forth with the call center assistants and still no resolution. I am so done with this service provider , now I cant do a sim swap because of my router.