mountain bike freewheel hub stopped rotating
Personally I think you have somehow managed to tighten the outer bearing cup that is part of the freehub body. It has two notches on either side, take the cassette off and see if you can knock the notches back to let the freehub spin.

If you have a Shimano hub you might want to also consider putting a new freehub body on there. These are LBS stocked parts albeit not an everyday request.

The bearings in the freehub can survive a bit of abuse, so long as you don't get too much dirt in there so consider DiY and, if that fails, pop a new freehub body on.