I dont freeze them,just takes heat,bit more than one might think. I use a propane sun heater,hold over till the case smokes and bearings just tap in. Tell more if you will on how you were doing it if you want,it should not be that hard. Heat is the trick,propane glow heater does it quick.
Freeze the bearing, heat the case to about 300. Use a small amount of thin oil or castor to help them in. No hammering required on any of the 50 or so 100's I've rebuilt, they usually just drop in, unless the bearings are off size chinesium. If they need help in, use a proper size socket that is near the OD of the outer race.
The key is to make sure they stay square to the opening. If they get the slightest bit crooked you will have problems. If you have already had one get crooked make sure there is no damage to the pocket for the bearing.