Outside of America, "cancelled" is always spelled with a double "l" because that is how it is used in British English, which is used everywhere in the world besides America. With worlds connecting due to the Internet and social media, one has to be aware of who you are talking to or writing for when deciding on whether to go for the double "l" or not.
In British usage, for words with more than one syllable ending in "l", the "l" is doubled before the addition of such endings as "-ed," "-ing," "-ist," "-ize," and "-ise." In American usage, the final "l" is doubled only when the stress falls on a syllable other than the first. American usage agrees with the British on annulled, controlled, patrolled, and extolled because the stress falls on the second syllable of these words. It therefore stands to reason that it should agree on "enrolled" as well, but one will often find "enroled" with a single "l" being used in publications.
Although people from all over the world use Facebook, the American usage is accepted by the administrators. That is why words that the rest of the world use "correctly" will be underlined as spelling mistakes under American usage. This has often led to great frustration and lengthy arguments by language lovers. We have to accept that there are two types of English, and that they are both correct!