All you need to say to them is, "Thanks but I'm fine. If I need your assistance I will gladly let you know."
If they don't drop it, tell them point blank, hey, is there something someone said about me that I'm being accused of? Because if not, leave me alone." You may be marked as someone that has a bad attitude, but what are they going to do? DF you because you don't need their so-called "help"?