Please reset network setting of both Sim one by one and than reset all settings of your's device in general management settings also Flight ✈️ mode on n off one time, restart your's device without any Sim in slots, interchange Sim in slots, turn off power saving mode then try to it's again. If you like please accept as a solution it's help to others users also, click 3dots in my reply section and click on accept solution. Thanks.
Check Data Roaming: Settings> Connections> Mobile networks> Data roaming to enable it, if disabled.
Reset network settings: Settings> General management> Reset> Reset network settings> Reset settings> Unlock your screen> Reset.
Check another network operator SIM: If the issue has not been resolved, then get in touch with the network operator and try to check with another network operator SIM. Note: kindly contact your network service provider once to make sure there is no issue from their end.
Update device software (If available): Settings > Software update > Download and install > Checking for software update > Software update available > Download > Downloading updates > Install now.
In case the issue still occurs, kindly visit the service center for a physical inspection of your device. You can locate your nearest service center with this given link: https://www.samsung.com/in/support/service-center/
