Let me add an important piece of additional information... I am assuming that you applied for a work permit extension before your work permit expired and that you also qualified to apply for an extension. Sometimes people apply for an extension to buy themselves time but don't actually qualify for an extension. In those cases, IRCC will sometimes return the application as incomplete vs. refusing, in which case the date the person was last in status is the date their original WP expired. In that case, if your original WP expired more than 90 days ago (and you applied for a WP extension without qualifying for one), it's possible you might not qualify to restore your status.