What can be done to correct ATM issuance mistake?

Requested $200 from a bank's ATM machine while at the beach. Only received $140 but receipt says I got $200. Bank refuses to accept my word that this happened and will not credit the $40.00 to my account. Is there an agency that can help since the bank indicates the case is closed? How would the bank know how much $$ was issued by the ATM?