spending limit increased without my knowledge

I spend R600 per month on my 2x Contracts with telkom mobile and 1x of them which cost R386 is about to expire in November 2015. The same R385 contract had its spending limit increased without know one notifying me and now i am sitting with a (R385 + R500) bill which I SHOULD PAY. Who gave you authorization to increase my limit as I didnt do that? I called the Call Center n reported this and they said they will look into it and a week later I am told this case (case no: ***4) has been closed! like for real now? I was not notified about the case been closed and yet you want me to pay for something I did not authorize. I want clarity about this cause I am done dealing with you people.