iMessage says "activation unsuccessful".

Some background, I switched to a new phone carrier today (First Net - AT&T powered). I had iMessage working just fine while using my old carrier (Google Fi). Since switching, it will not let me activate Facetime or iMessage and gives me a popup saying "An error occurred during activation. Try again." It has a check mark next to my email/apple ID but as soon as I try to tick my phone number, this message pops up. There was another recent forum on here about this but I did not see anyone provide a solution or update. Please help!!

*I have an iPhone 12 Mini with the updated iOS14.6. I have tried the following "solutions":

-Restarting phone, including restarting it after turning iMessage/FT off

-Logged out and back in from my apple ID. (Attempted a restart with my ID logged out as well)

-Reset network settings. (attempted a phone restart as well)

-Resetting the phone and backing it up with an iCloud backup.

-Turned airplane mode on (and of course restarted the phone)

My cellular works just fine. It is not an issue on the FirstNet end of things. I can text normally and make phone calls, use my internet, etc. Literally just affecting iMessage and Facetime with my phone number.