Given that a "drabble" is a story of exactly 100 words, what can stories that have more or less than 100 words be called? There are a few terms in common usage that can be used to describe such stories.
Anything over 20 000, and we're approaching novella territory, but if a fic is approaching novella territory it's unlikely to be mislabelled.
"Flashfic" in particular is an excellent term that should see more usage. Most fics that are mislabelled "drabbles" are actually flashfic.
(This list was derived in part from this discussion on Fanthropology and this article.)
Dear [Author's Name],
As a concerned member of the Drabble Protection Society, I notice that your story, which has been presented as a "drabble", in fact contains more or fewer than 100 words. Its actual wordcount is [wordcount]. Since a drabble is a story of exactly 100 words, this story would be more correctly presented as a [flashfic or shortfic/nanofic].
I would like to draw your attention to the incorrect usage, and respectfully request that you correct it. This is not intended as a criticism; sadly, many people are misinformed as to the correct definition of "drabble". However, in the interest of preserving the clarity of the language, it is important that this word, which has a specific and unique definition, not be used in place of other, less precise terms.