Hi, and welcome to the community
Obviously, the first thing to check is your volume levels. So, when in a call, press the volume up button to the desired level. Try putting your phone on speakerphone too and see if you can hear callers.
If you have wifi calling activated, then ensure you have a strong wifi signal. Try turning off wifi calling temporarily, and perform a test a call.
Contact your network provider and ask them to troubleshoot, too.
Try a hard reset
With the device powered up, Hold the Volume down button and Power button simultaneously for 10 seconds. The screen will go off. Continue to hold buttons until the device vibrates and the Samsung logo appears. Release buttons. Device will reboot. Once done, please check if the issue is resolved.
There's also a diagnostic you can perform via your Samsung members app. Just head to the Support section and tap on Diagnostics.
