Contract dispute

I took out a contract with telkom through mondi sales last year june, instead of 1 they posted 2 cell fones. I called for months so they can take back the other fone and no one attended my quiry. They over charge me and expect me to pay for both fones hence i only use 1. The sim card has been blocked since august and i refuse to pay for two fones i dont use. They keep debiting crazy amounts montly on my account. Legal wise called them on my behalf, they promised to collect the fone and nothing is done but they debit money for it. Plz help