Fix mobile data problems
First, check that mobile data is turned on and you have a data connection.

Open your Settings app Settings and then "Wireless and Networks" or "Connections" and then Mobile data or Cellular data. On some devices, you may need to select "Data usage" before you see this.
Turn mobile data on. If it's already on, turn it off and on again.
Check that there is a data indicator (for example, 2G, 3G, 4G, H) next to the signal strength bars at the top of the screen Signal.
Note that sometimes this will not display if you have an active Wi-Fi connection. If this is the case, turn Wi-Fi off and check back.

If you don't see a signal data indicator, you may be in an area without coverage. If you can, move to a different area (for example, go outside) and check your signal again.

Note: If this happens a lot, contact your mobile service provider.


Next, turn airplane mode on and off.

Open your Settings app Settings and then "Wireless and Networks" or "Connections" and then tap Airplane Mode. Depending on your device, these options may be different.
Turn airplane mode on.
Wait for 10 seconds.
Turn airplane mode off.
Check to see if the connection problems have been solved.

If you still have problems after you complete these steps, contact your mobile service provider.
https://www.necticon.com.ng/fix-internet-connection-problems-on-android-devices/

Whether you call it cellular data or mobile data, its importance doesn’t diminish. When you lose connectivity, it often feels like life has stopped or one is lost. Communication, knowledge, and fun are all snuffed out. This walkthrough explains how to fix Mobile data not working on Android.

https://www.novabach.com/how-to-fix-mobile-data-not-working-on-android/