Vodacom not cancelling contract and crediting my account

I have been phoning Vodacom since January to cancel one of my lines I am not using. I have now phoned four times. Spending about 30 minutes on the phone. I was promised that it was cancelled and that I would receive a credit for the amount incorrectly billed. I was also promised a reference number that I would have received via sms after the calls to confirm that it was cancelled. Till this day no such reference was received. I have been a loyal customer for years not missing one payment. This is extremely disappointing.