How can I make phone calls on my iPhone 11 after having retrieved it from lost mode? Found it via Find my iPhone

How can I make & receive phone calls on my iPhone 11 after having retrieved it from lost mode?

Several other functions are working. I can take pics., access contacts, use my calendar, make & receive texts, but I am unable to make or receive phone calls. I have an important phone appt. & need to be able to make calls. It's my only phone.