Problem: No mobile data service on Galaxy A8 (2018) (SM-A530F).
Background: My mobile (cellular) data stopped working completely when I switched network providers from Plusnet to EE about a week ago. I can't get any mobile internet connection, even when I have four bars of signal strength. The handset doesn't show a 4G+/4G/3G icon near the clock. On the SIM card status menu, "Mobile network state" shows disconnected, even when mobile data is enabled. Voice calls and wifi data work correctly. Mobile data used to work correctly on previous carrier (Plusnet). Latest software is installed (build PPR1.180610.011.A530FXXULCUK6).
Testing SIM (my SIM works when in my wife's phone; her SIM--also EE--works in her phone but not in mine.)
Calling EE, although the fact the SIM works in another device implies it's not the network
Switching airplane/flight mode on and off again
Checking "Data saver" is off
Checking "Set data limit" is off
Restarting in safe mode
General Management > Reset > Reset settings
General Management > Reset > Reset network settings
General Management > Reset > Factory data reset
Deleted and manually recreated APN
Installed "Samsung Members" app, and ran diagnostics tests (no errors found)
Deleted cache partition and formatted device using recovery mode