Vodacom ignorance

i went to colonade vodacom in april to get my monthly bill reduced, they talked me into a upgrade they said it will come down from R2700 to R2300 after a month and by Septembet it will be R1600.This did not happen my bill went up to R2928 . I also got a new sel no that i did not asked for now they claim i should have read my contract . I was led to belief one thing they gave me the wrong information and according to that i made a upgrade .no one in vodacom wants to hear me the shop owner just gets sarcastic with me and ask me if she must pay my bill for me?