This particular scam received coverage in the Daily Telegraph last week and Barclays Bank are aware of the issue so contact them quickly.
This is a warning for everyblody to be very careful about signing up for trials of free products online using your credit or debit card, as cancelling the card doesn't necessarily cancel the ability of the supplier to continue drawing money from it.
If you're a regular online purchaser you may wish to consider getting pre-paid cash card simply for your online purchases. You can add whatever amount you like to your pre-cash card but once it has been emptied it is not connected to your bank account and so no further drawing can be made from it.
Also be very careful when buying things like insurance & magaines online, as you can often find that the small print commits you to having annual premiums or subscriptions taken from your card every year unless you specifically opt out.