This line totally works.

Had a hospital visit after being rear ended. Long story, but it took a while to get the insurance information from the other driver, so I said I'd pay out of pocket and be reimbursed, just to send me a bill and I'll send the insurance information over if I get that first.

I got the insurance information and sent it to them, everything they needed. I got a bill in the mail about two days later so I assumed it had just been sent out prior to me contacting them. No problem. I called them, asked about it and offered to pay. They said no, disregard it - it had been paid.

Two months later they came at me with the same bill, saying I owed it. I called them out on it and had records of every conversation I'd had with every person I spoke to regarding the incident.

I told them I had no obligation to pay anything after I was denied months prior. It was the exact same services for the exact same date that they told me had already been paid. A week later they dismissed it.