Conundrum with Payment from Prior PM

[Manco Snead]

Greetings, 

Conundrum here; had a PM for an OOS property for 6 months. In short they were horrible and I lost thousands of dollars because of them, mostly due to a non-paying tenant they never properly dealt with. I terminated my contract with them 2 months ago. At the end of the contract they sent me my final distribution of $1,500, but they accidentally sent it twice. I called, out of my good integrity, to see what was going on with this; they basically said everything is fine. Even though I thought it was likely a mistake I then just kept the money, having made my attempt to be honest.

Two months later they write stating they caught the mistake and they want one of the $1500 amounts back. I'm furious at them for the money loss and headache they caused me and half of me wants to keep the money. The other more honest half, along with fear of reprisal, says just send the $ back.

Do they have any legal recourse if I don't send it back?