im not happy the way they billed me

I have been Altech Autopage customer for a year and 3 months I have a contract with them so for two months I didnt pay cause the screen was brocken I have to fix a tab then 3rd month I pay they diactivated ny sim card which I was not using then for +-8 months I didnt use the sim card then I call them to activate it for me so that I can use the data that I didnt use but im paying for it. To my surprise I only get 3 gig from 2 previous months ands for the month I call them to activate then I used it around 25 the 3 gig was finish they give me on credit for a week to my surprise there comes a bill i must pay R2554 I call them ask them but why I must pay that kind of money I try to explain what happened its not my fault that I get 3 gig tue lady who was assisting me gave so my question is I only use additional data for 5 days and they charged me R1554 as im paying R774 per month which is is not a problem now again they charge me R554 for the month of October on top of that R1554 I called them what response I get they need me to pay the money without letting me explain whatcreally happen to me its a ******* and their consultants are rude one put the phone down while I as trying to expla