Burning plastic smell in cabin after catalytic converter was replaced

Hello all-

I recently got my car back from mechanic after having had the catalytic converter stolen. When I brought it home, I spray painted it bright orange with a high heat spray paint after having read that can help deter theft. The next day when I stopped driving I smelled a burning smell, took another look at the spray paint can, and realized it was only for up 600 F or so, and read that the cat can get up to 2,000 F. Now I am smelling a burning plastic smell only when I have the air intake set to outside air. My question is: where is the air being brought in from the air, and could the paint on the catalytic converter be the problem, or could be there was other damage done in the theft or repair? Can anyone point me to a chart of where the air is brought in, and where it goes to get warm and ultimately reach the vents? Does the air tubing go near the catalytic converter? It seemed to me that I smelled it more with hot air or AC air than cold air. I don't smell anything when the air is turned off or on recycle. Thanks for any help in advance. Basically I'm wondering if I should even try to get the insurance to cover fixing the issue, or just admit that it was my fault and attempt to get it fixed myself. Either way I'd like help on trying to ID and understand the issue.