Medical bill that I was paying on sent to collections?

Have medical bill that we were paying on sent to collections. The amount sent to collections did not match our records. Sent validation to the collection agency and they just sent a statement with charges but did not answer the questions I had to verify the balance of the debt.

Called the hospital. Told the person in patient accounts that I disputed the balance. Turns out there was an admit that took forever to get paid--long story. Turns out they applied the last payment to that co-pay-she stated that we were never billed for that which was their mistake. And understood why we disputed the amount. She also stated that the account should never have been sent to collections. She offered me a discount if we paid the balance immediately and she would call the collection agency to return the account. Asked for this in writing, after she hesitated she agreed.

Did not receive the new bill with statement that we settled. I called Monday to see what happened. This same person denied she the agreement made in our previous conversation, but she sent the statement. I informed her I made notes of our conversation and read them to her. She then said I misunderstood her and she would send another one to me. Asked her again to put the agreement in writing so I could prove to the ca that an agreement was made. She agreed.

Called yesterday to ask if she sent the new statement and written verification of the discount. She said she sent the statement and a sticky note to the collection agency of our agreement and it was up to them to decide if they accept the discount and it was out of her hands. Asked if it was out of her hands why did she offer the discount. She said she did not know the account was sent to collections. Told her that that was not true and again read my notes to her. She said she would talk to her supervisor and get back to me.

I have not heard from her today and she will not return my calls. Any suggestions here?