Odd Phone Call; Phishing

My mother and I were just talking amongst each other about random news, when she was Called by a VoIP Bot. It did it's normal practice, waited a few seconds, then the automated message played.

What was weird however, was when she Hung up. Her phone Kept on Vibrating, and Ringing as if they were still calling her. No matter what we did, Calling, Closing out Apps, going into new Apps, it would perpetually continue, it would even refuse to use the sound engine on other apps. Apps such as YouTube would have no sound, with a message that basically said the sound engine was being used by another app. There was no call though, no pop up. Just her ringtone going off, and the phone Vibrating. She thought it would break her phone, so she immediately restarted it, before I could record it.

Can scammers add malware to their calls now? Did they find a new way, to accost people on a personal level? I figured it might've been a Glitch on her phone, but after many attempts to replicate it, we couldn't. The phone is a Samsung Galaxy A23 if anyone was wondering, or wanted to run their own tests. The phone is also, extremely minimal in downloads, aside from things such as Facebook, Chime, etc, no other apps have been downloaded.

I just find this, Odd. Very concerning though.