Vodacom is failing Customers

I have a wifi router that I got on promotion for R160 for 20gig every month 2 years ago. I never changed my wifi after 2 years as I was happy with the wifi and just decided to carry on with it. After 2 years of religiously paying 3 contracts with vodacom, I received an invoice now for the exact same wifi for R900!! I never once received a call or a message to say that the amount of R160 will now change to R900...how are they allowed to invoice me that amount without my knowledge or approval? I phoned vodacom and they told me the promotion ended, hence the new amount, but there is a current promotion of R199 for the wifi if I'm interested?!! So I asked Yvonne at vodacom why would I then be paying R900 for wifi if it's only R199, so she said because I didn't give my consent??? But I didn't even bare any knowledge of this amount increase so my consent was not given to pay R900. Uncapped WiFi is R399, who in their right mind would charge customers R900 for 20gig wifi. It's disgusting. How many other customers are they doing this to?