Silence unknown callers does not work as expected - iPhone XR / iOS 15.2.1

I have two numbers, and I have enabled Silence Unknown Callers in both.  Unfortunately, my phone still rings - about once every 30 minutes - with a spam call.  In fact, I have not received a single call yet from someone I actually want to receive a call from - just endless spam, all day, without end.  

The problem is so bad I may have to uninstall the application entirely.  

Attempts to disable notifications in the notifications section also do not seem to work.  I had hoped this would disable all audio notifications, but neither the banner nor the audio is silenced when a call comes in despite having silenced the app in iOS notifications.

Only the Do Not Disturb function in iOS will quiet it, but this is a device-wide setting I can't realistically use during the day.

In the past few hours, I notice it rings exactly one time.  I do not know if this is a matter of spammers hanging up (only been a few hours), or whether having turned on the Silence option, this is now the resultant behavior (one ring only, but that's one ring too much.)

Some more time has passed.  It appears that it now rings exactly one time while the Silence option is turned on.

iPhone XR / iOS 15.2.1 / MySudo 1.13.1.20211112100239

Your diags report the Device model as iPhone 11,8