Medical Bill on my credit after paying in FULL!!

[mypenplease]

ok so here is the deal,

 

about 5 years ago I went to the hospital. There was a small balance about 200-300 remaining from what the insurance didn't pay. The billing department says to me, they will settle this for about 50% $150 bucks-or-so, so I pay. BUT!!!! THESE GUY WERE MORONS!!! Denver Health, these pieces of chocolate's don't know their flowers from a hole in the ground! SO, I tell them before paying I want a statement saying settled an PAID IN FULL! Flash forward about 4 years later, I get these deadbeat collection company that is listing this bill on my credit, never heard from the collection company, nothing.... I contact the collection company, they do nothing... I dispute the bill with equfax, their findings "it remains on my credit". So now after a few months, digging a copy of this bill up - I have a copy of my bill with the Paid in full, and the charge from my credit card and I am not sure who I should contact first or what I should do. any ideas?