Valvoline Broke My New Car

Location: Missouri (Saint Louis County)

I went to get an oil change at a valvoline I don’t usually go to because I was in the area at the time. The people in the shop didn’t seem to be paying much attention to anything, a lot of talking to eachother about their lives, throwing stuff at each other, no communication with me or other customers, except for payment. When I hopped on the highway, my check engine light came on flashing, and the car wouldn’t pick up speed/lagged, so I pulled over to the side.
I didn’t get home until 1AM that night, and missed work the next day.
I took it to the Mazda dealership/service department, and they told me Valvoline put way too much oil in my car. So far, I need a new catalytic converter, and they have given me a starting repair quote ~$8,100.
The mechanic said that’s where they need to start, and then they need to make sure there isn’t oil elsewhere/further problems. I, or Valvoline, needs to pay the repair estimate first, and there may be something else that was affected.
I just bought this car on my own last year, and I was excited to have a nice reliable vehicle, and planned to have it for another ten years at least.
I made a claim with Valvoline, but I’m unsure how this will go and if they will pay everything in full. I’m doing this all on my own, and a bit concerned I’ll get screwed somewhere in the process.
My brother said to consider hiring a lawyer, but I wouldn’t even know where to start, and very likely it would be out of my budget.

I’m not sure what to do or ask for at this point.