§ 13. Cancellation of consent. When a consent to the plan shall have been filed in the office of the county clerk as herein provided, it shall be binding upon both parties thereto as long as the relation of employer and employee exists between the parties, and expire at the end of such employment, but it may at any time be canceled on sixty days' notice in writing from either party to the other. Such notice of cancellation shall be effective only if served personally or sent by registered letter to the last known post-office address of the party to whom it is addressed, but no notice of cancellation shall be effective as to a claim for injury occurring previous thereto.