I have simple model, just legs and pants, when pressed play animation pants mesh goes up to the pined mesh part. I played with cloth simulation and collision values but result always the same.
I have made some changes. Also cranked up the quality settings a bit so if your pc can't handle it, just pull those back a little. I have pinned the top and some other simple settings. I also changed the shape of the legs very slightly so the pants wouldn't pass through on some places. The edited blend file