FaceTime and SMS messaging temporarily went to an unknown user

My dad has an iPhone 11 with a phone number that is part of my Verizon account. I FaceTimed him on the usual number, and a stranger answered. That stranger then texted me FROM MY DAD'S VERIZON PHONE NUMBER, "You are calling wrong person." I called my dad on his landline and asked if he could FaceTime me. He successfully FaceTimed me FROM THAT SAME NUMBER. Then I asked if my dad could send me a test text FROM THAT NUMBER, and he did so successfully. Now, in the text chain with my dad, it's me and my dad for, like, two years, then a rando text, "You are calling wrong person" then me and my dad again. I'm about to embark on the project of changing my dad's Apple ID, which given that he has never used it for anything and doesn't know how to unlock his phone, promises to be a project.

Verizon's best theory was: Someone between 11:00AM this morning and 3:45PM this afternoon was forwarding my dad's apple I.D. to another device then turned off call forwarding when we connected.

Apple's response was: The text was sent from a Verizon SMS phone number, not an apple I.D., therefore, it is Verizon's problem but I should reset his Apple I.D. just in case.

Both parties agree that the phone cannot be cloned and the phone itself is not likely hacked. (To be frank, there's literally nothing on my dad's phone to hack. He doesn't use it for anything except calling me.)

As I have now spoken with 3 incredulous tech support people who have reviewed my account and the texts in question and are FLUMMOXED, I throw it out to the Apple Community. What? How? Why? Please and thank you.