All they need is your phone number to text you. Obviously that is not hard to find, and some people make it easier with insecure habits.
Don't reply to them; delete them, or alternatively create an address book entry and add the numbers to it ... I have one named "Spam Telemarketer", with about 80 numbers on it so far.
The benefit of that is you don't need to deal with repeat offenders, plus if the same number ever calls you again, the Call Display will be Mr Spam Telemarketer (or whatever first, last name you choose) so you know to ignore it. You can also then set a smartphone to use a unique ring tone, or no ring at all, or put them in your ignore list so the call or text won't ever reach you at all. You have many choices as to how to deal with it, in other words.
Even though the sender's number may be spoofed ... means fake ... it's still worthwhile to note that number. What spammers do is they will seek out unused or un-assigned local numbers and then use those as the originating number. They can enter and use any number they want; that's a basic feature of Skype or any computer-based calling application. So, for example, they could be calling from Russia but the number you see on Call Display has a Colorado area code.
If you reply that just marks you as a "live" number. To be a little less than polite, that basically means you are an idiot and they will step up efforts to scam you, plus when they sell lists of numbers the ones that have replied are worth much more money, essentially guaranteeing your number will be on that list and guaranteeing an increase of scammers calling you.
Do not reply if there is some link or other indication that you were called by mistake and to have your number removed from their list. This is of course just another means to get you to reply, mark yourself as an idiot, and get put on the list of people most likely to be scammed. DO NOT REPLY, PERIOD.
They do this at Xmas time because it's a time of year when people are more likely to expect annual communication from lesser known people. This is "Social Engineering", the number one most successful means to get people to give up information. Even highly trained individuals get caught by this ... on average about 30% of people fall for a Social Engineering ploy. Recently the San Francisco Transit Authority was broken into by hackers. The means was a Social Engineering eMail sent to all staff with an eMail address.
The staff at SFTA were well trained ... 90% recognized it for what it was and deleted it or forwarded it to IT staff for investigation. But 10% didn't and replied to the link in the message, meaning the hackers had many times more replies than they needed to break into the network. All 10% of those who fell for the ploy were trained to not fall for the ploy yet they did so anyway. That is why these scams still persist ... they work.
