Automatic blocking of private numbers
In Android, we can automatically block calls from private (or hidden) numbers. You can enable this from the app settings -- block numbers -- turn on the block private numbers switch. Note: when blocking a call, in most cases the caller will be automatically directed to your voicemail, without knowing that he/she was blocked.
In iOS, Navigate to settings page >> Call blocking & Identification
- Switch on the toggle so that you will not receive calls from numbers reported as spam. Tap on "Add New" to add a number to the block list and tapping on the blocked number allows you to unblock it from the list.