All you have to do is call in the morning. They count the cash every morning and will see they have a $50 overage. They will credit your account.
You should have gone back with the receipt as soon as possible to speak to the Bank Manager. There are cameras in the ATM 🏧 lobby which would prove that you were there and MCU should reimburse you the missing $50. (Before I leave the bank, I make it a habit of recounting and verifying the exact withdrawal amount because I know technical & computing errors can be made and also that thieves have been tampering with the MCU 🏧. 🤔)
Thanks! Your answer is awaiting moderation.