Fomer Employer Paid 1mo Salary

I know I am legally resposible for getting them the money back but I am insisting that they reverse the transactions rather than just withdrawing the money from my account and handing it to them but they are saying that it's not posisble and they want me to just hand them the money. My concern is regarding the tax implications and if I hand them the money that no one will lift a finger to do anything about it after. I say this because that is the culture they keep, its a group of greasy gas station owners, doing as I mention would be far from the worst i've seen while employed with them.

How should I go about this?