Legal Question in Business Law in California

Whether it's "legal" or not could only be said with certainty after looking at the subscription agreement. Sometimes newspaper subscription agreements are written in terms of weekly or even monthly units, and sometimes there is a provision requiring a brief notice period for a cancellation to become effective. More likely than not, however, this is just the result of unintentional error by the newspaper's subscription department. Someone misspelled you name, or forgot to notify the carrier, or something. The most effective handling would perhaps be by telephone with either the subscription or accounts receivable departments at the paper. I do not know whether the paper would report non-payment of a small balance to the credit agencies, or if it did, how the report would affect your credit score.