Trying To Re-Caulk Bathtub

OK, trying to recaulk bathtub. Having trouble getting old caulk out. Old caulk does not appear to be silicone. It is extremely hard, and cracked. Sections of it are completely gone. It's the same color and consistency as the grout in the tile. Bought a Homax Caulking kit. It ate the plastic blade before I was 1/4 of the way done. Bought another caulk removal tool with a design similar to the Homax, except it's metal. Scratches the hell out of the tub. Bought some Motsenbockers Caulk Remover. Instructions said let sit for 3-4 minutes. I gave it two hours. No good,