Tucks Tire & Muffler Center

2 months ago, my spouse & I took a Nissan Altima to this shop. I left it over the weekend, he would check it & call me. It would cost $500-$600 if it was the converter. I told him I'd use them as I checked the price at Nissan which was more expensive. He called saying it was the converter for $713. My car ran worse. I took it back. The guy said he never checked it before replacing. I went over the events of a week prior. He said I told him to replace it, the dealership checked it. We argued. My car was kept over the weekend again. The owner called with a transmission code but had cleaned the air flow & throttle body, now drives fine. I get my car, same issues. I call the owner, he says I told them to replace it because of the dealership. I explained my spouse was right there with me, none of that happened. He said that isn't what his guy said. Nissan replaced the transmission; they said converter is not new, it was cross threaded leaving a leak & the old one was hollowed out.