I was billed twice for one transaction

I bought some items for an amount of R599.90 on the 22/08/2015 and as I was making a payment the slip from speed point shows approved but the invoice for my items did not come out. I was asked to pay again, I asked how come cause it was approved by the speed point, they did all the checks and said they did not receive the money. I logged to my internet banking and showed them it has gone through. They told me I will have to pay still and gave some excuses and so on. They promised to refund me if I send them a proof that I was billed twice. I sent my bank statement to Andrew, he was going to deal with it and give me feedback in 24 hours. After couple of days I called him, he told me he was on leave and will ask someone else to deal with my query. Today is 09/09/2015 I never heard anything from Edgars. No one bothers but I still want my money...