Lawyer letters go a long way. If it doesn't work, you can probably file a small claim in your local jurisdiction (w/o a lawyer), since you entered the contract with them while you were physically in said jurisdiction. If they don't show then you win whatever you asked for, so be sure to ask for a higher amount than they owe you for this reason, but not excessive or you'll look like a fool in court. For example, included all of your shipping costs even though you might not get them from a judge. Tack on anything possible but not unreasonable.
The only problem with going to court is that it might be difficult to collect, i.e. have to contact their local sherrif's department and have them show up and collect for you, possibly in goods rather than cash. That is, if they will honor a local decision, etc.
Filing a small claim should not be too expensive and if you win, you'll get your court costs back. This is all based on my local laws, so you could ask the lawyer about it (i.e. this is not actual legal advice blah blah). My old landlord didn't know what hit him when he tried to steal most of my security deposit. He brought his lawyer and still lost, against myself and my old roommate w/o lawyers.
