bad service and breach of contract

I app**** for a contract in August 2015,the agreement was 24 months,the amount I agreed to pay was R104.99 the agreement was that I receive 2 gigs of free data monthly which I have been paying until I was billed with R2218.17 in February 2016, on the 15 of February 2016 I queried the billing and they forward proof of usage and was advised that I had a limit for R2000.00, which I never app**** for consented for.On the 18 March 2016 I requested proof of when I took a contract for 2000,they said they will listen to the call recording and get back to me,but to my surprise no one came back to me and now I have been handed over for collections. When the collector call me on the 3 of April 2016, I asked her if my query was resolved and she hung on me.