Although this happened to me about a month ago I just noticed this site. I am with Sainsburys and had a Vodafone transaction for £25 on my card last month. I have had my money refunded and have had to fill in fraud forms so they can investigate.
I also had a transaction for 19p (yes that is right!) for the WA Ballet in Australia on the same day as the Vodafone transaction.
You post stood out because you have used Shopto just like I have. I only use this card on 2 sites: Shopto and Microsoft's Marketplace for the Xbox 360.
This is very concerning that you should reference the same online shop as I use.