So go to court... its not a big deal, the wost that they can do is give them a judgment against you... that they can use to garnish your wages... which would suck, but its not the end of the world.
The most likely result will be they will appear, and ask you to accept a settlement offer. When I went through this they didn't even send a lawyer, he was an intern! I still accepted the settlement as it was 1/3rd they were suing for, and about $100 off the actual amount I think I owed (they tack on all those fees, etc. to scare you.... FIGHT BACK!)
And with everything else, don't take their first offer, if any... most likely they will accept payments in their settlement offer.
Trust that it costs them more to actually go through with the suite. settlement is good for them, not great for you, but better than losing. If you have good enough reason the debt is invalid, then put it in the hands of the judge... but if your excuse is you can't afford it, well that won't fly... that's what bankruptcy court is for.