Hi @celsog ,
how strange! Would you be able to try the following things?
1. Turn the phone off, remove the SIM card, and give the golden contacts a rub. Once done put the SIM back and test the phone.
2. Does the problem occur in all the areas and with all your contacts? If so, turn Flight Mode on from the quick panel. After a few seconds turn this off and check if you are able to do calls.