Galaxy A8 (2018) Mobile Data Stopped Working

[Members_DECexHu]

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).

Already Tried:

1. Testing SIM (my SIM works when in my wife's phone; her SIM--also EE--works in her phone but not in mine.)
2. Calling EE, although the fact the SIM works in another device implies it's not the network
3. Restarting device
4. Switching airplane/flight mode on and off again
5. Disabling wifi
6. Disabling Bluetooth
7. Checking "Data saver" is off
8. Checking "Set data limit" is off
9. Restarting in safe mode
10. General Management > Reset > Reset settings
11. General Management > Reset > Reset network settings
12. General Management > Reset > Factory data reset
13. Deleted and manually recreated APN
14. Installed "Samsung Members" app, and ran diagnostics tests (no errors found)
15. Deleted cache partition and formatted device using recovery mode

I'm at a loss. Is there anything else I can try?

[BandOfBrothers]

@Members_DECexHu let a Samsung Service Centre have hands on with your phone to assist by assessing it.