Removing a stripped(?) bolt

[WestCoastSVX]

Need a bit of advice on how to get a couple stuck bolts out. I'm assuming they are stripped or somehow messed up either on the bolt threads or the threads they go into but not sure, this is a new one for me.

A couple of the bolts under the front of the car that hold the big plastic under cover on. The cover has long since fell off when the holes tore bigger than the bolt heads over time. But the bolts are still in place and just spin freely in there. I've tried putting extreme downward pressure on them with vise grips while at the same time trying to unscrew them with a ratchet, but again, they still just turn in place forever. They seem to be stuck in place, free to sping, but neither able to tighten or loosen beyond the point they are at.

And now even more exciting, one of the bolts that holds my driver's seat in has done the same thing so I can't remove my seat either!