Has anyone ever called Frankenstein Frank before in any movies, books or other media? Or has Frankenstein just been called Frankenstein?
I can't trivially prove that Bugs Bunny has called Frankenstein's Monster "Frankie" (as alluded to in a comment by James McLeod; however, I can prove that another character with a similar sense of humor has:
In the early to mid 1970s, Marvel Comics published The Monster Of Frankenstein. And, as they also published Marvel Team-Up, they had Spider-Man meeting all sorts of characters (some licensed, some public domain) also being published by them at the time. Spider-Man had met the likes of Dracula, Fu Manchu (and his son, Shang-Chi), Doc Savage - and, inevitably, the Monster.
Spider-Man met him and teamed up with him in Marvel Team-Up # 36-37 (cover-dated August and September 1975 respectively, with a Spider-Man-related werewolf character named Man-Wolf being the "official" team-up character for # 37).
The only surprising thing here is it taking until page 6 of the second comic for Spider-Man to actually call him "Frankie"!