If it's your state refund, it's not as common to have a refund increased, but it's possible. You really need to find out which tax agency sent it in order to know what to do. You can look in your bank (or card) account to see who it was from.
If it was directly from the IRS, it will likely show as from the US Treasury.
If you paid any product fees out of your Federal refund, however, then it will show the payer as a third-party company.
If the IRS reduced your refund, they will send you a letter in about 3 weeks explaining why. Or you can phone them. I'll leave more info and the steps to call them in an answer below.
