How do remove a concrete filled 3 inch pipe embedded in my garage concrete floor which is 2 feet tall and was intended to prevent cars from hitting the water heater which is no longer in that location?

How do remove a concrete filled 3 inch pipe embedded in my garage concrete floor which is 2 feet tall and was intended to prevent cars from hitting the water heater which is no longer in that location?
You will have to break out a small area of the surrounding concrete first. Then you will use a Heavy Jack and Chain to pull the pole out of the ground. If the chain will not stay fixed when wrapped several times around the Pole, you may have to drill a hole through the Pole and put a Rod or Bolt through to secure the chain.

Or, you can contact a concrete cutting service. They have boring saws that will easily deal with the thickness of the concrete of your garage floor (after cutting the pipe off). Takes about an hour, is so much easier, and leaves a much smaller, easier hole to fill.