My iPhone calls go dead at 90 seconds.

iPhone SE 2nd Gen:

I suspect an internal iPhone setting has been altered

• My SE performs beautifully except for phone calls
• Incoming/ Outgoing mobile calls go dead at precisely 90 seconds: every time
• My carrier is T-Mobile and some of their Verizon towers have not been updated with T-Mobile tech but I get 2 to 3 bars which is normal for north FL
• FB and Netflix apps work well
• I Have 12 available Gigs for free use
• I clear my Web-browsers daily
• I execute a ShutOff/On twice(double-boot) each AM and PM
• PLEASE recommend which Internal iphone Settings I can review to ensure that my iPhone settings have not been altered.
• NOTE: “Cellular Data” ‘Options’ cannot be found any longer - Last year, I could choose LTE or 4G options: that screen no longer appears.