It may not seem like it, but you sort of hold the power here, given the arrangements made by your lawyer and senior management above your boss. You outplayed, outmaneuvered, and outthought him, and he has few cards to no cards to play. That leaves screaming, intimidation, insane demands that are left to him, and he is leveraging that to the max.
Senior management is likely sick of all this already and wants to wash their hands of the whole thing. HR won't help because you lawyered up. That you managed to triumph against all of them made you no friends, and your presence reminds them of their defeat.
So what to do? First, alert your lawyer - clearly they negotiated well and understand the dynamics. Maybe it is in everyone's interest if they reward your full pension early, for example, literally solving their "problem" in one fell swoop. Nine months to full pension does not seem that long really, and everyone would be happy to end this standoff. Management hates mess, after all.