Help!

We are hoping to buy a house in the spring and I got a collections letter from CPA.  They stated that they hadn't reported to CR and that I should pay soon so that they do not.  I did a quick gut reaction and just paid it, out of fear, to prevent that from happening.  I have credit monitoring and nothing had reported.  Of course, a week after I pay, they report it.  Paid collection, zero balance.  I could cry.  My credit score has dropped 25 points.  This IS a valid debt, it slipped my mind, I forgot about the stupid cable box, and here I am.  

Too late to DV, too late to PFD.  GW is all I have, correct?  Where will I have better luck?  CPA?  Comcast?  Any specific route with Comcast?  BBB?  

I'm frustrated at the fact that I did the right thing by paying it and they STILL reported it after the fact.  I should have known better.  I'd have 200 more dollars in my bank account and the same credit score had I just let it be.  And maybe a shot at a PFD.

Any advice would be immensely appreciated.  I have no idea how this will change our ability to buy a home with a collection under 12 months old.