How are mice getting in buick encore ?

Mice can get into almost anything and only need a very small hole to do so. Look for holes in your firewall and in the floor etc. A window left down a 1/4" would be enough.

I had similar problems on a KIA Sportage and a Hyundai Elantra, even had one die somewhere in the Elantra, couldn't find it. I put a small piece of screen wire on top of the cabin filter located behind the glove box. This completely solved the problem. I have now put one in the Encore. All three cars made or designed in South Korea. Do it now.