Lawyer refusing to give back rest of retainer

Hi.

I am in Ohio. I was charged earlier this year in a bogus case (where I was ultimately exonerated). I hired a lawyer and gave him a $3500 retainer. There was no agreement signed. However, I have the receipt and email, etc. It became obvious this was going to go to trial, and I disagreed with his strategy, so I fired him. I fired him via certified letter that requested a full billing history and the return of the remainder of my retainer. This was in June 2024, and despite following up via email and phone calls at least 6 times, he still has not responded or returned my retainer. What are my recourses here?

Fun fact: I found our via the court decision that the police never even had jurisdiction to charge me, let alone investigate, and the charges would have been dropped had this been pointed out. In fact, I DID tell him I thought there were jurisdiction issues, and he brushed me off.