The op has, hopefully, learned a valuable lesson: don't work without a signed contract.
That said, the comp should have just paid or, at very least, tried to negotiate the amount thought I don't think that's worth the effort either. This is such a paltry amount as to not be worth the effort to fight.
People have reneged on signed contracts. A signed contract is not a foolproof protection for your payment. You just have a better case when going to court, which will cost you money. Also a verbal agreement is a binding contract.
The thing is, this can (and sometimes does) happen with larger and better established businesses too.
A common rule of thumb in the design industry is that if the amount of fees in question isn't going to be worth going to court over, then a 50% deposit paid up-front is a reasonable request.
That said, the comp should have just paid or, at very least, tried to negotiate the amount thought I don't think that's worth the effort either. This is such a paltry amount as to not be worth the effort to fight.