On my birthday, I got two texts from people I don't know, wishing me a happy birthday. I initially thought they were legit, just not in my contacts, but when I responded to the first two asking who they were, a third text from an unknown number came in within a minute.
So, yeah, shouldn't have responded.
But if someone already knows knows my number and my birthday, what do they stand to gain from my response?
Now they know the number is valid and is worth money to sell to marketers.
I get these periodically as well, but mine usually say "Who is this?". Best to simply delete them I figure.
My birthday is January 1st, unless it's the IRS or someone verified legit that's asking. My DOB is just one more piece of my personal data the Russian mafia doesn't need to know about me.
Just because you're not paranoid doesn't mean they're not out to get you.