Have they done the same to everyone who has had abscences? or are they treating you differently?
Have you had much time off since the first notice? If not don't worry about it too much. They can't really pull you over the coals if you haven't had time off since March! What can they say? "Five months ago you had sick time so you're fired???"
By refusung to go would (to me at least) show that you had little respect for your employer (even though they were a bit lacks). Which would in the long run not do you much good!
It could be that the new HR manager is sorting out what should have been done and it is mearly a formality, possibly to make sure any future action is above board.