In case of default in the payment of an installment or call when payment is due, the corporation may proceed to collect the amount due as any debt due the corporation. The bylaws may prescribe other remedies for failure to pay installments or calls that become due. No remedy working a forfeiture of a subscription, or of the amounts paid on a subscription, may be declared against a subscriber unless the amount due remains unpaid for a period of 20 days after written demand has been made. If mailed, written demand is considered to be made when it is deposited in the United States mail in a sealed envelope addressed to the subscriber at the last post office address known to the corporation, with postage prepaid. On a sale of shares by reason of forfeiture, the excess of proceeds realized over the amount due and unpaid on the shares shall be paid to the delinquent subscriber or to the legal representative of the subscriber.