I said bullhorn.
A bullhorn will allow you shout until you run out of breath or batteries.
Bullhorn:

But seriously, that interruption technique is a favorite of theirs. Piers Morgan was famous for that. And quietly saying, "May I finish, please?" does not usually work because you're operating on the
invalid assumption that you're in polite company, which you ain't.
I heard one interviewee allow the anti-gun interviewer to keep talking. When he finally finished, the interviewee said absolutely nothing for a loooong pause. Finally the interviewer asked "What do you say to that?"
The interviewee said. "Oh, sorry, I didn't realize you were done interrupting me."
I laughed my ass off over that one.
Another technique is changing the topic when you present a cogent and valid point.
A not-completely fictional sample:
You: "But the Second Amendment is not about hunting."
Them: "What about the children? You can't have yahoos with guns running around the schools willy-nilly!"
They have a lot of tricks up their sleeve. Pro-gun people used to say "I can't watch Piers Morgan," but I always found it instructive to analyze his (and others') techniques.
Terry, 230RN