Original Creditor and Collection Agency Lied? What are my Rights?

I received a statement for an account in January that I thought wasnt valid I promptly sent the Collection Agency a letter asking them to send me the statement from the hospital to see what the balance was for. Towards the end of February I finally receive the Statement and find that the account was indeed valid I had just not received the statement from the hospital. So I received the statement at the end of February and receive a letter from the collection agency on March 8th stating that if I pay the settlement amount that I accept the offer and that the hospital and I agree to release each other from all claims related to the charges for the collection. I pay believing that everything would be okay. I had until the 23rd of March to send the payment which I sent but found out that they reported me to Experian on the 4th of March. I had no prior knowledge of this account I did not know what it pertained to and the account had to gotten to their collection agency. Im adding more.....