Laptop charged twice on credit card and not refunded a month later

I have bought a laptop in Oct 2018 for +- R13 000. During checkout, there has been a time out and the payment had to be reprocessed. The next day, an HP consultant phoned me to enquire if the intention was to buy 2 laptops or if there had been an issue with the order. I explained the issue and was told they would refund me the second payment. Upon receiving my credit card statement 10 days later, no refund was made and I was indeed charged twice. Phoning has proved useless: Sihoe told me (6 Nov) that he would get back to me - to no avail Stanley told me (7 Nov and a day later) that financial dep would process refund and I would receive proof by email. Stanley again (22 Nov) told me that they did the refund (which the bank denies) and that he would send me proof "immediately". This is completely unprofessional. While I have no doubt I will eventually get my money back, I will have to pay an extra R13000 towards my credit card this month, not counting all the time wasted trying to phone and email HP.