Double debits, unreturned funds

I started a new smartplan 100 contract with Telkom for which they debited R599 from account on the 3rd of Dec. Apparently I was supposed to get this R599 back as the transaction only served to check if my details are valid. I see no reversals. I have now received an invoice which charges me for Dec and January usage meaning Telkom has simply taken the initial R599 into their back pocket. I have since contacted Telkom twice and they say they are unable to view the same invoice they sent to me. Either ensure you sort out your billing, return my money or if theft is how your system works,nullify our smartplan agreement and take back your device before the debit order runs off my account. I cannot call telkom again only to be told the invoice is not visible, I hope telkom will find this missing data and call me back.