Odds are their computer will straighten it out shortly.
People a been prosecuted for taking the money and running when a $10 deposit ended up being $10 Million,.
It would have been decent to point out the mistake at the time, but you can always claim ignorance - just do not spend the extra $80 - because it will be reversed in a couple days.
They will find out there was a mistake. Don't spend more than the 80 dollars that should be in the account.
they will think more of you if you call and tell them of their error. they WILL find the problem in a couple days and correct your account, but calling them will assist them in locating the mistake and they'll remember that.
It will be "your mistake" if you do not bring it to there attention right away.
Yes, its theft by fraud
yes, it is called stealing