iPhone 12 problem hearing incoming calls

My new iPhone 12 has a problem- I can’t hear incoming calls but I can hear calls that I made-

for example, someone is calling, I answer and neither one of us can here anything. Just silence.

than I hang-up and call back and this time everything is ok- we can hear each other and talk normally.

it has nothing to do with reception.

I have a normal SIM card.

can you help and tell me what’s wrong with my iPhone?

thank you.