Your best bet, short of filing a small claims suit, which is a minimal cost, is to just walk away and chalk it up to experience. One load will cover that 500 bucks. You will likely lose far more than that trying to collect. If a company develops a reputation of doing what you describe the word will get out....
I agreed and I think is this is the best approach ever.
Count the losses and and learn from it. Think about the countless hours, days, months, or may be even years you will waste you energy, time, and money on this merely $500. Those times and energy can, instead, be utilized in planning and finding new opportunities that might translate into 1000-fold of future incomes
Sometimes emotional factors can work against our good judgements. Learn to let go of those emontional burdens. Your thinking will be clearer without those emotional monkeys on your shoulders.
If all else fails, change your thought, consider that you are making the donation to the company. Which in turn, your donation will feed those little mouths that belonged to those staffs. As they say, a good deed is always rewarded....10 times the reward.
May prosperity be with you.