ZRod

Did you try kicking it and swearing at it yet?  Do you have a family?  If so, have you tried blaming any of them for the problem and making them really uncomfortable?  After that I am all out of ideas.

Dynamite. 

You can cut/saw the flange (without damaging the pipe) and start trying to get a chunk out of it and then work your way around a chunk at a time. Usually the glue joint will come apart and the floor flange won’t want to stay adhered to the pipe. Usually you can wedge a straight screwdriver between the flange collar and pipe and it will separate. But yeah, it’s a PITA and might take awhile. And I did say “usually”...