"Cellular Data Options" is not visible and data is not working

Issue: Data does not work. If I open apps or safari, I am told "could not activate cellular data network." Apps say I'm offline. iMessages do not send. (SMS send and calls go through. )

Background: I switched carriers recently and activated new service. They asked me to update to the latest iOS 15.4.1 on my iPhone XR. After doing so, my data does not work. iMessage does not work and I have no data access. This is not location-specific.

My Phone Settings: When I go to Settings>Cellular I see "Cellular Data, Personal Hotspot, Default Voice Line, Cellular Plans, and then a listing of cellular data for primary (apps), then wifi assist, icloud drive, call time statistics and reset statistics.

If I click on "cellular data" I only see "off, primary (my number which is checked), and "allow cellular switching" is greyed out (locked).

I CANNOT see anywhere the "cellular data options" everyone refers to, nor can I see any place for LTE settings, because I cannot see "cellular data options."

Help is appreciated. 5 days of this and the carrier's folks can't get it worked out either.