I just had the floors in my bathroom replaced and now the flange is too high. When I put the toilet on top, the front touches the floor, but the back does not. The flange and piping are PVC, and the floor is concrete with vinyl on top. I'm not sure how to approach this problem. There are many solutions for a flange that is too short but not for one that is too tall.
Unfortunately, with a flange that is too high, you typically have two choices-
There is a third option that sometimes works, and that is to use a waxless sealing ring, though they tend to be leaky, and it sounds like your flange is too tall even without the ring.
Depending on how the flange is coming up through the floor, and the access you have from underneath (Though with concrete I am guessing you have none) you may be able to remove the flange, cut the pipe shorter, and put a new flange in.
I found this 2 part video on YouTube that helped me understand what to do.
I ended up cutting off the top of the flange with a PVC pipe cable saw. I then used a mini hacksaw to cut some segments into the fitting and wedged the pieces out. After removing 2 small parts of the ring, the rest just wedged right out without much effort. I cut down the pipe to be flush with the floor using a pull saw. I put a level down and found the concrete was not level around the pipe. I used a rub brick and the mini hacksaw, which I could angle to cut the inside of the pipe, to get the pipe and surrounding concrete truly level with the rest of the floor. This took a while.
When I finally got it level, I put in a Twist N Set Closet Flange. I drilled 4 pilot holes and put in concrete screws. The toilet is now level and not going anywhere. Now I just have to fix my guest bathroom which has the exact same problem. At least I got a good deal on the house.