"Do Not Disturb" is useless for blocking unwanted calls

I'm getting dozens of spam calls a week. I cannot individually block them as they are always from a new number.

I have my do not disturb settings as follows:
Manual - On
Scheduled - Off
Allow Calls From - All Contacts
Repeated Calls - Off
Silence - Always

Ideally this would block all calls that are not in my contacts at all times, and it does but the problem I have is with notifications. I cannot find a way to allow notifications (text, email etc) from contacts (or otherswise) be allowed through while blocking calls at the same time. As it stands I can receive calls from contacts but everything else is silenced. I would like to be able to receive calls and notifications from my contacts as per normal while blocking all calls from numbers not in my contacts. This is extremely frustrating as iOS doesn't seem to allow this functionality through settings or apps. Please inform me if I am missing something. The way I see it I have 3 options to achieve my goal. 1) Jailbreak my iPhone to allow apps that are available to other users 2) go back to Android next upgrade 3) change my phone number

Thanks in advance