bad service for contract

I took a contract fro Vodacom for 2 years after a year they stopped deducting without me authorizing the cancellation but they kept on deducting money from my account ridicules amount I have tried speaking to them on telephone, e-mails but no luck, this month alone for I contract of R300 that I took back then they deducted R1561.82, now when I go out to seek credit it shows that I owe them I need this to be sorted out as this is stressing and give me a bad credit record, Vodacom is the one that owes me not the other way around. would you please assist.