If they are bothering you say "Thank you for being nice to me, I am going to say this in the most the nicest way possible, but you're kind of bothering me right now. If you keep messaging me/ bothering me I'm going to have to block you" or you could say "Please stop asking me for my insta/snap if you keep asking me I am going to have to block you. Thank you have a nice day :)"
you could say something like that