Debt Validation Letter?

I would. The original creditor (hospital) will have all the paperwork necessary to prove you owe. The collector might not! Debt is sold to them but rarely do they send the paperwork that you signed. If the collector can not prove it's your debt then they must remove it from all three credit bureaus. It's a chance you take.

Yes, I would still send the DV letter to the collection agency. First off, validation MUST come from the original creditor. The collection agency simply cannot print up a paper showing what they claim you owe and call it validation. Proper validation must come from the original creditor's files. Secondly, there is always a chance that the debt collector could violate the law (FCRA, FDCPA or state law) and you could use that violation as leverage to negotiate down the balance or even make the whole thing go away. There is really no downside to sending a DV letter. Yes, some people claim that it might make you a target for a retaliatory lawsuit (if your debt has not passed the statute of limitations) but as long as you don't word the DV in an overly hostile tone, you should be perfectly fine.

what are you trying to do/not do?