Charged twice for 1 transaction, no response to customer support email

I have used Zapper successfully in the past with no complaints. On 16 September, I used Zapper and I received a "declined " notification. I then used my 2nd card which is linked to Zapper, and this was approved on the app. On checking both credit card statements subsequently, I have been charged by both cards, so the decline notification was incorrect. I then emailed customer support, to date no response has been received.