I got my tax check in the mail when I opened it I realized they gave me more money then I thought I was getting back over 400 dollars more.

A few days after I got a notice in the mail sent to my home address (I moved and have yet to change address right away) My grandpa opened it for me and was reading it.

From what I got it said refund.. but then I had to return the extra money. But no action has to be made on my part.
When I called the number he gave me on the paper it stated :

They determined I was entitled to a tax credit due to new tax legislation (spelling?)

What is the new tax legislation and would I have to send back the money?

Please help! Thank you.

IRS letter will have information on why you got the extra money. It may be Making Work Pay credit of $400. Ask your grandpa to read it again for you.
If IRS letter says do nothing, do nothing.

Thanks!