Vodacom billing

Vodacom has a double payment of mine. I was told they would refund me the money of which I never got a cent back so I left it thinking it would cover my next bill to be told I still owe them over R 400. I'm sick of all the problems I've had from vodacom I've had to call them every month for the last 4 months. To top it off my account is more every month. It's ridiculous.