Valid Collection Agency???

I have a medical debt from 09/2011 that i have been making payments on monthly. (not with approval from speaking to anyone.....just mailing in small payments here and there monthly) They have went ahead and turned me over to a collection agency. I have a balance of $150.74 left and i received a letter from FMA Alliance with the typical "you have 30 days to validate the debt" and have offered me a settlement of $113.06. And they have requested i make the payment directly to the hospital. Should i contact them and agree to the settlement or is this a trap that will be put on my credit file. it is currently not on there. Should i ask for a PFD letter even if it's not on my credit yet? This is my first question so thanks so much for the help. I have been quietly stalking the forums gaining much needed knowledge.