Go to Settings >> Network & Internet >> SIM cards to select the preferred SIM for cellular data

Ensure you are dialing correct phone number and area code

Issue may be with poor or no Network. Try dialing again or  go to another area where network are strong

Reinsert the SIM card

Check with another SIM card, if you are able to make a call or not.

Try changing the Network operator search and check again.

Go to Settings  >> Network & Internet >> Mobile Network >> Advanced >> Network >> Automatic select network/ Choose Network

If Call barring option is activated for the phone number you are dialing, then contact to SIM Operator to deactivate it.

To check call barring option : Go to Phone >> Settings (three dots on the top right) >> Calling Accounts >> Select SIM >> Call Barring >> Select desired options

Go to Phone >> Settings (three dots on the top right) >> Calling Accounts >> Make calls with >> Select Operator (SIM 1/ SIM 2/ Ask first)