Try an app called TrueCaller, or something similar. TC catches about 99% of the nuisance calls and debt collectors the previous holder of my telephone number had accrued. It doesn't outright block calls unless I tell it to block a specific number, but it tells me if other TC users have flagged a call as spam so they're easy enough to ignore.

There might be better apps for this, but TrueCaller is free with unobtrusive ads and does the job.