Sorry to hear this and sadly there are some real losers out there who think that they can just blag their cash, benefits, TV, etc without having to work for it.

Don't stress about it, though - neither her or the amount of cash involved is worth it.

Is there someone else at work, that you both know/respect, who could be an intermediary? If not, it wouldn't be unreasonable to tell any other workmates what has happened so they don't make the same mistake as you, though this gets quite close to slander territory and could come down to your word against hers.

I don't think the phone abuse, signing on to mailing lists etc is the best way to solve this, as it most likely won't get your cash back even if it does give you some satisfaction, but if you do go down that route it may be best to let some dust settle first so she doesn't know it is down to you.