Contract overcharged

Worst experience with telkom my data contract billing is R450, now its gone up R570, when i called to asked one of their call agents told me, its subscription done and i only use that sim for modem and when i asked for proof they say the system cant really show exactly. Called them again their call centre agent said its a technical glitch from their side and it will be fixed in the Next 72 hour, nothing as yet, and then i was told that i need to call again following month again cause there’s another technical glitch that will only show in the end of August invoice, why do i need to call again, why cant they fix it cause they see it before hand,they keep saying matter will be escalated and still no change in the billing invoice, what they are doing is *****, i pay their money in advance, now i feel their finding a way to ***** from clients on the name of subscription ( yet no trace of mobile device), day light ******* pls help.