Vodacom taking my money from my account

I cancelled my contract in November and ported to Cell C. Vodacom is still billing my account. I phoned to query it and they said there is a 079 number (that I have never heard off) that's being billed. Upon further investigation, it was found that Vodacom issued a Ghost sim to me without my knowledge. The call centre agent transferred me to the cancellations department to cancel the sim which they said the did and I was told that the billing department would be in contact with me with regards to crediting my account. I tried following up today and was told that I need to go to the police station and make an affidavit and supply bank statements.