Had an issue with the Data Access Network when I changed SIM card. Did all the fixes stated including Network Reset, reinserting SIM, etc. Fix was that the SIM card was still somehow linked to the profile that was set on the previous SIM card (used in the Japan). Fix was to go to Settings/General/VPN and Device Management. Delete the profile that is linked to the old SIM card, in my case Docomo. Rebooted and fixed. Have an iPhone SE.