Small cluster of pimple like calluses on the bottom of my heel that hurt when pressure is applied, tried using a pumice and woke up with swollen heel.

May: need to see a Podiatrist or your PCP for debriding of the callus and evaluation

Unlikely a callus: Things that cluster like that are likely a planter's wart and need to be treated as such. Your pumice action likely just irritated it & will make it spread. See your PCP for confirmation and treatment.

Mosaic verruca.: Typically, callus doe not appear in clusters, especially on the bottom of the heel. It is more likely a mosaic type wart that will most definitely spread with pumicing. To remove all doubt have your heel examined.