Please follow the Quick Start Guide.

go to Settings > General > Profiles > delete any installed APN profile (if present)
go to Settings > Mobile Data > Mobile Data Options > Mobile Data Network
Enter APN globaldata (one word small letters no spaces) into sections Mobile Data, LTE, and Hotspot if available.
Delete username and password if present.

Please restart iPhone.
After restart please check next:
Data Roaming enabled
3G mode enabled (turn OFF 4G/LTE, voice and data only option)
WiFi and HotSpot feature OFF
Mobile Data OFF/ON

Wait up to 3-5 minutes for constant 3G mark/signal in an upper-status bar and then check the connection, for example, open Safari and check
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