So how is one supposed to answer to a misdirected text? Out of all the ways to handle it, politely letting the offending party know what happened is the kindest route you can take. Typically, they will probably either apologize and immediately cut ties or send a novel filled with uncertainty and insecurities. So if you choose the noble route, be ready for the consequences.

But if you're positive you don't know this person, so can use the prime opportunity to... be a dick about it. If that's what your heart demands, of course. However, remember that there's a real human being with real feelings on the other end and you have no idea what condition their mental state might be in. And, of course, they have your phone number. So naturally, there are limits.

When in doubt, a simple "sorry, I think you have the wrong number" should (hopefully) be enough. But if things start to get out of hand, you can always call your service provider and have that particular number blocked.