There is no spam block feature that is directly available in any iOS version. What there is, are many apps available claiming to block spam calls. Your carrier may even have an app doing the same and available through the App Store.
What I am not sure about is whether you have such an app on your iPhone that you activated OR did you simply turn ON Silence Unknown Callers feature that is available within iOS 14.
I suspect that you may done the latter. Let's double check that and see whether that resolves the issue.
Open Settings ➔ Phone ➔ Silence Unknown Callers : Set this to OFF.
Axel F.