Actually there isn’t a catch. Verizon corporate rep here…The promotion is getting a new line of service with a free device. Free being that if the phone is $23.05 a month, you will see where you are charged $23.05 a month and the credited $23.05 a month for 36 months.
If there is a “catch” I would say the phone being free is contingent on you staying with Verizon for 36 months to be credited for the device payment. You paid sales tax upfront which is typically all that’s required. Welcome to Verizon!

I work for Verizon Wireless. Go to your carrier and get a new SIM card and see if that fixes the issue. That’s what I would start with if you brought it to me.