Hi! Welcome to the Samsung Members community!
Signal bars are weird. Signal is related to your provider, not the device. *99% of the time
Search on Google if your SIM provider is having network issues, or contact them directly.
Troubleshooting may also help:
* Restart device
* Take the SIM out and ensure it is free from debris
* Settings > General > Reset > Mobile data-related settings.
Also, be sure to go to the Samsung Members app > Support > Diagnostics. Does it show an error? If so, contact Samsung Support.