I would. Contact them again and again until you get a response. Don't give up. Send an email once every 3 days.
For 2 weeks, if nothing happens.
Send an email EVERY DAY until a response gets to you. I know you're told to not spam people, especially like TomFulp, but the point is exactly this. Start to irritate them, start to step on toes. Scream and yell until this is brought to the right person.
Inform them that the project they have sponsored has been done so illegaly. No confirmation or arrangements were produced for use of the songs.
It is important to highlight that what just happened is in good standings for legal action should it come down to that.
It depends on how far you want to go. Some people don't care about the money generated from such sponsorships, but I tend to go as far as I can without any real ramifications to force the flash artist to watch out for whose lawn they're planting their dandelions. Trying to steal or ignore terms can and will in the long run screw them big time.