I can just smell the smugness wafting over from some of the posters.
It might not be this particular situation that stings you, but this is only one of hundreds, if not thousands, that parents/children face most days.
Ours was getting DD (12 at the time) a phone and finding she'd been talking to some internet random. I/we take responsibility for not being as tech savvy as we thought we were setting up the parental controls, but everyone knows how fast technology changes from one year to the next, just look at how many social networking websites there are that are in fashion one minute then another comes along.
I try my hardest to keep a track on what DD's up to online (especially in light of what happened (had a thread about it at the time which was invaluable and got CEOP involved, who were as brilliant as the posters on MN were) but I've said no to DD having accounts on twitter, keek, snapchat, instagram, skype, and youtube when she's asked. She's on facebook but all the emails go through one of my accounts and she knows I have access and will look at what she's up to.
It's endless, and she's only 13! What's it going to be like in another year or two?? 
Saying no to the phone/internet/social sites isn't really an option, especially when teachers say they can mess about on their phones when they've finished their work in lessons! WTF? It's just a given that they're online.
I hope you do get the money back OP, and I'm glad there's more sympathy than condemnation on the thread, you definitely don't deserve any shit for what's happened.