Iphone 7 Blocking numbers mysteriously
There are few things to check before you can make sure numbers are automatically blocking on your device. 


Go to Settings  > Phone > Call Blocking and Identification and
check if you find the same number which you think is blocked?
Also at the top you'll see apps that have access to call blocking.
See if there is any app that is automatically blocking numbers?




If your answer is NO to both questions then you should check with your phone carrier and see if there is any problem in your phone network.