iPhone 12 Pro Max Unable To Activate

Hi so I started having some issues a few weeks ago with my iPhone 12 where it kept dropping service and then picking it back up again until after a few hours it completely stopped connecting and it started telling me I needed a cellular update but didn’t give me any idea where to even start to fix it. I went to 2 different Verizon stores to figure it out and they switched my SIM card and did a network reset, nothing. One of the guys told me that because nothing worked I should backup and factory reset, I did and now it’s at the “hello” activation screen and once I get to the step of connecting to WiFi, the next screen says unable to activate and it only gives me and option to shut down. Any help or insight is so greatly appreciated. I need answers because this is not making sense to me and I need my phone. Please help