Problem with my telkom 24 months contract

I have taken a contract from southgate telkom outlet for 24 months with Telkom for 160GB..means 80GB night..and 80GB for R239...a month..the 1st month i paid R239...which was fine...the 2nd month..they deducted R249. ..which i was now suprised..the 3rd month..they deducted..R269...i was not happy..and i went to southgate telkom outlet..to find out why...their explanation was not ok...because they even told me that the next payment will be R703..which i could not understand..then they say they will phone me as i was not happy..and i wanted to cancel the contract...because it was not what i signed for...i waited for their call..but they never phoned....they never also gave me my contract..i am not happy..i need them to sort it out that i must pay what i signed for or that i cancel the contract