Thanks for your response yet again!
I have checked and I am indeed the account owner. I have enrolled all 3 of my lines in the past (2/05/19). We all received text messages on our respective lines/devices and I too received one on my line on 2/05/19, when I first enrolled my line in the 6-month trial. Despite this, I am still stuck in the endless "Joined through Verizon? Verify your line" loop that results in me getting nowhere and no ability to use my Apple Music Subscription.