Freewheels gets screwed on by pedalling torque, so getting them off ca be a challenge.
tip #1 is to stick the puller in a vise bolted to a bench bolted to the wall/floor. Then grab the wheel as if you're driving a bus and go at it.
tip#2 is to lock the puller in place with a wheel nut, support the wheel against a wall, get the tallest tool you have and go at it. Remember to back the axle nut off as soon as the freewheel has started moving.