Source : Sims Direct
If your phone says it's connected to LTE or 4G but the data isn't working, try to manually turn off LTE/4G to connect to 4G/3G.
Apple:
Settings > Mobile > Mobile data options > Disable LTE > Restart
Android:
Settings > Connections > Mobile Networks > Network Mode > Switch to 3G/2G > Restart
It might look different depending on your device! If these instructions don't match exactly, explore your settings until you find Network Mode
When did you activate and what happened when you activated it?
What troubleshooting steps have you tried?
Please send through a screenshot of your Mobile Network settings and your APN settings with the WiFi turned off and your mobile data turned on so we can see what's going on.
Any other details that might help us, help you!