Not just denied.
If they had denied it then, hey, that's their prerogative, the party is a private entity that can do whatever the fuck they want.
What was fucked is they strung protestors along telling them they'd get to speak, then pulled out at the last second when there wasn't enough time to react.
If they weren't going to let them speak, they should have said it.
But bald faced lying to avoid the optics of a protest is billshit, and why people don't trust Kamala. She shot herself in the foot and then got mad her boot has a hole in it.