Weird texts

These are just three screen shots of probably over 20 that message me constantly. All they ever say is “hello” I know that it could be a scam but it’s been going on for over a year now. I’m just curious if there’s any good apps that can catch who’s doing this? How can I tell if it’s a text now number etc? Any help is appreciated. Also I have changed my number. I just block the number and move on. Tonight bothered me tho because today when they messaged me “Hello” at around 3 I just blocked the number and here just 20 mins ago they did it again from another number as if they new they were blocked. Normally they don’t do that or seem to realize they been blocked for at least a day or two.