Space cell mounts

My space cell 3 came with these round mounts for the board and the screws. Getting them in the board was a pain, first drill holes in the deck, then epoxying the mounts into the holes. But I just try to unscrew the screws and some of them tore through the epoxy and now seem impossible to get out. With a power drill, when I try and turn the screws, the mount just turns with it. And because they are round mounts, it is hard to get a grip on. What should I do?

screw one of the bolts in and pull/hammer

Those are through-and through? Take a nut and put it on the bolt, screw this bolt from the other side and then tighten the nut until it is flush with the deck. You now have a lever, use a wrench from this side to hold the mount and unscrew from the other.