Claim no payment when payment show on my phone

Me and my wife bought items worth R303.00 from Lichtenburg Checkers. I paid with my Debit Card and it registered as paid on my Mobile Phone and an email came through to my phone confirming that it has been paid. The cashier informed me that the transaction was declined. I showed her that the transaction as paid on my mobile phone and her answer was that is happened a lot and that we must pay again because it will be reversed during a day or two. I got angry and refused to pay again because I have proof that it was paid. The Supervisor \Sara"came and told me the same story. I refused to pay again and she went off and spoke on the phone. After about 10 minutes I was called to the phone and spoke to somebody that"