74. In the case of a contract for the loan of money or of an open credit contract, the consumer avails himself of the right of cancellation(a) by returning to the merchant or his representative the net capital, if the consumer received it at the time at which each of the parties came into possession of a duplicate of the contract, or the part of the credit extended already used; or
(b) by either returning the net capital or the part of the credit extended already used or sending notice in writing for that purpose to the merchant or his representative, in all other cases.