I got a message after buying movie tickets on fandango.com about getting $10 cash back. I clicked and somehow signed up for "Reservation Rewards". I did not re-enter my credit card info. After getting a few emails, I didn't really think much of it until I got charged $10 for the membership--if it had said when I signed up that I was going to get charged, it wasn't clear at all, because I definitely would not have done it. Not only did I get charged, but it happened when I had less than $10 in my bank account, resulting in a $38 overdraft fee.
When I called my bank, the customer service rep said he'd seen a lot of these charges recently, and I can tell it's happened to a lot of people. I called them, calmly explained my situation, and they were actually receptive. I asked them to please refund the charge, and when I told them about the overdraft fee, they said they would refund that too. They actually followed through on both...I was shocked. If you've had the same problem, try calling them and just explaining everything, and hopefully it will go well for you too. Definitely make sure to be calm and nice to them, it can't hurt when you're dealing with such sketchy people.
When you call, make sure you get a cancellation confirmation number! They will want you to fax them a copy of your bank statement (I printed mine off the web and blacked out everything but what pertained to them), make sure you be as specific as possible, reference the time you called, who you talked to, etc. Hopefully it goes well, I definitely learned my lesson in clicking on web offers.