removing the bottom bolt on the bracket from the compression tube
This part of your post leads me to think, that you have a bolt, without a nut on the other side of the mast, that goes through the mast inside a compression tube. You can not get the bolt to slide out of the compression tube. The C-tube is designed to keep the mast from collapsing as the bolts and nuts are tightened. Dirty and perhaps corrosion has seized the bolt.
If this is the case, you need to try and get any chemicals into the space between the tube and the bolt. This may be an impossibility.
You might try force. Replace the nut on the bolt end. This could provide a target. Then use a hammer to pound the bolt loose in the compression tube.
All of this may be complicated by trying to do the work while suspended above the boat. I suspect it would be much easier with the mast laid on supports at ground level. You turn the mast on its side. Gravity helps fluids flow down onto the bolt and into the compression post. Any force can be more controlled.
Good luck.