My Fed. refund received is 3156.00 more than it should be. Where should I call to report it and find out what happened?

You will need to call the IRS at 1-800-829-1040.

I suspect there was a tax payment made on your behalf either through withholding or applying a prior refund, that was not reported on your tax return.

When more or less is sent the IRS will send a letter of explanation in the next couple of weeks so wait for that letter ... and be aware of a scammer that may contact you with instructions on how to cash the check and send funds "back" ... the real IRS will never call or email you  only send snail mail.  You can try calling but you may be on hold for hours and not get an answer.