My work experience includes house moving and raising buildings for additional height or to sit on a new foundation. It may be cost effective to have a contractor to simply detach your existing garage, raise it up and reattach sitting it down on what is called a pony wall. It need not be a House Mover company to raise your existing garage. It really is not complicated or that big of a deal. If your existing garage is not attached to a different structure it is easier yet. If you do raise the garage, I suggest you raise it to have a 14 foot door. Very little additional cost, you will not make the mistake you made the first time.
Wayne