I’d recommend reading this if you are interested in why making assumptions when designing a system is a bad idea (but often necessary): https://github.com/kdeldycke/awesome-falsehood
Especially the one on names: https://www.kalzumeus.com/2010/06/17/falsehoods-programmers-believe-about-names/ And the one on time: http://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time
Never answer, the scammers sell data to each other. As soon as you answer, they know they’ve got a live number and the number of calls will multiply.
Also there’s millions of them, pissing off a couple doesn’t really do anything.