Both forms presented below are correct.

Correct spelling

cancelled

Correct spelling, explanation: cancelled is used in British English. According to the rule, in case of the word ending with consonant-vowel-consonant combination, the last consonant is doubled when a suffix is added. Thus the British spelling is cancelled (cancel plus -ed gives double l, hence cancelled).


Correct spelling

canceled

Correct spelling, explanation: canceled is the American spelling. In Noah Webster’s 1898 dictionary this spelling has been approved, as well as many other American spellings, which were the simplified British spellings.

Definition of cancelled/canceled:
verb, past form of verb cancel, to annul or eliminate something
The concert was cancelled due to COVID-19 epidemic.
It was snowing all night so today’s classes are canceled!