What is our recourse when an ATM accepts cash, cancels the transaction but has no record of it?

My Son deposited money into an ATM and it accepted the cash but it said "transaction cancelled." It did not give him a receipt. This happened on a Saturday night. He called 'customer service' right away and they told him to go into the bank on Monday. On Monday, he went into the bank and they said that they had opened up the ATM but did not find the $138 that my son had deposited. They said they were going to look at the video. This, however, has been over 2 weeks ago and they keep saying that the video is not available yet. How could this have happened and what is our recourse? Thanks!