How to Handle Debt Payment Fraud?

What are my rights with a debt collector?

I made an agreement to pay off a medical debt in six months at $103 per month, with the 1st payment coming on Sept 30th and the second payment on Nov 1st. The final four payments would come out on the 1st of the remaining 4 months.

The first payment came out on Sept 30th as planned, however, the second payment came out 3 days later on Oct. 3rd.

I called my bank and informed them of the error and they stopped the payment. Then I called the debt company and informed them of their error.

They said that was the agreement we made over the phone, so I asked to hear the phone conversation and was denied. I continually informed them that I never agreed to pay on Oct 3rd nor had I defaulted or cancelled. They eventually put me on hold so long that I hung up.

What can I do at this point and what are my rights?

Should I try and get the original $103 dollars back that I paid on Sept 30th and cancel the plan??

Thanks,
Concerned American Citizen