If the device recognises your SIM card and you can make calls/SMS (and receive calls/SMS), but you do not have internet, you may need to configure an APN (Access Point Name). Go to Android Settings/Network & Internet/Mobile Network/Access Point Names and click on the plus sign to add the APN. Don’t forget to save (top right menu) once you’ve set the APN details.
You should contact your mobile operator for details on how to configure the APN.
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