I'd start by contacting your bank. Happened to me a few years ago and turned out the bank knew there was a problem with a certain petrol station - they were running a scam and the police were building up a file to prosecute (the petrol station guys were running mobile phone top up cards through with every transaction and pocketing the proceeds). The bank immediately gave me a refund... and three guys at the petrol station went to jail. Whatever happens, the bank are best placed to advise you on what steps you need to take.