Both forms presented below are correct.

Correct spelling, explanation: cancelled is used in British English. According to the rule, in the case of the word ending with a 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, 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 simplified British spellings.

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