If you unable to receive calls from a specific phone number, you should check the list of the numbers you have blocked. Conversely, if you can’t make calls to a particular number, you have to ensure that he/she hasn’t blocked you! You can check it by calling from another number!
Some technical issues don’t allow you to make calls. A simple restart can fix the most common issues, but sometimes you may need a reboot to make the device problem-free.