Most “apps” that help you block calls are just a game of whack-a-mole. People call you, and if you don’t want them to call again, you add them to a block list. This puts you one step behind spam callers. They just change their number and you’re helpless again.
Some apps add in the ability to share your block lists with a community of other users. This helps, but it’s still a game of whack-a-mole…just with more hammers.