MANY years ago, I sent off my tax return and realized the next day that I had made a BIG mistake. I called and asked what to do. They told me to submit another tax return with the correct figures and write AMENDED RETURN in red at the top of the return and also write it in red letters on the face of the envelope. So I did just that.
A couple of months later, I got my tax refund for the incorrect amount (too much). Two days later, another check came for the correct amount. I called IRS again and asked what to do with the incorrect check. Just hang on to it, I was told, until I got a letter asking me to send it back. So I did. A month passes, two months, three months, no letter. I call again and am told the same thing. Four months, six months, 9 months, a year. I call again; same instructions.
After a couple more months, I put the check in an envelope and sent it back registered so I could prove they got it. I never heard anything about it.
I often wonder what would have happened if I had cashed both checks.......