iPhone 13 Pro Max froze during a long voicemail, preventing call end or access to settings

I received a phone call from an unknown number. It showed they were leaving a voicemail but it seemed to last longer than normal so I ended the call. They called back & started leaving another voicemail so I thought I’d let them leave one. It went on way too long! But I didn’t have the option to end the call the 2nd time. I turned off my wifi & cellular data because when I went into settings I couldn’t click on anything. I tried using the external buttons to turn my phone off but they wouldn’t work either. I got my son to look at it & I did not know that when you use the pull down screen from the upper right side that the little icon in the upper right corner would shut it down. He did that and it worked. I remember the area code was 701 I believe. But I don’t have a voicemail from them nor does that number show up in my recent & missed calls. I have no idea how they did that & that’s the only time that has ever happened. I have no idea if they were able to get some of my info or what that was about. But now I’m worried about it happening again. If anyone knows how they did that, if there is a way to prevent that from happening again, and what they were doing I’d love to know. Thank you in advance for any help!

[Re-Titled by Moderator]

Original Title: iPhone 13 Pro Max was locked up by incoming call that was leaving a voicemail but does not show a voicemail or a recent call from that number