Usually a repeating overpay of this sort is caused because notes have been placed into the wrong feeder - so that where there should be 10's the person refilling the machine mistakenly puts 20's.
As well as the valid CU argument bear in mind someone could loose their job over this but that may be less likely if most of the money is returned.
This could only happen with US Dollar notes because all are the same size. Anywhere else in the world this is physical impossible as feeders are adjusted to the size of the notes.
If you want to withdraw 500&, recepit(500$) and the account was decreased with 500. The ATM gives you 100$ free, then enjoy your free money. We shouldn't have mercy for banks!
Stealing from a thief still makes you a thief. Any way you look at it it's not your money, you don't have the right to steal.
Nothing has been stolen, OP has called the bank to find out if they mistakenly gave her more money as they should have.
I would say OP mind is already on holiday.
If it would have happened to me i would not have know as i just put it straight in the wallet and that's it. Equally if they short charge me i would not know.
It has happened in the UK several times so the hoppers won't be as tight a fit so as to prevent wrong stacking. In these three cases the customers were told they could keep he money! No legal basis to enforce repayment? Would be took much bad PR? Too much trouble/non-compliance asking other banks for interbank customer details?