If you still can't make or receive calls, contact Apple Support and follow the steps to complete the request. Turn your phone into airplane mode, wait a few seconds, and then turn it off again. Take a look at the Do Not Disturb settings. If it's on, turn it off again.
If your iPhone isn't making or receiving calls or texts, there are a number of variables that could be at play. The most common problem is that you could be in an area with no cellular coverage or with a weak cellular signal. Apple's own support site has a useful document that explains the details of the procedure, but basically the iPhone will first try to connect via the last Wi-Fi network used. With the standard repair, the data on the iPhone won't be erased to fix the iPhone not making calls, but I can send text messages.
When your iPhone was unable to make a call, the first method you should try is to turn airplane mode on and off, which can restore your iPhone's network connectivity. It is very likely that the problem is not in the iPhone itself, but in the settings of the iPhone or the network. Many iPhone users complain that my iPhone doesn't make calls but sends text messages, so it's not convenient for them to contact other people in time.