We issue Notice CP12 when we correct one or more mistakes on your tax return, and: The overpayment is different from the one you expected. Complete your protest and mail it to the IRS address on the letter that explains your appeal rights.Many find the easiest way to figure the entries for Form. X is to first make the changes in the margin of the return they are amending. You generally have 30 days to respond to an IRS notice, so there's no reason to ignore it. Always check which tax year the notice relates to. The primary letter we use to request information about a return is Form DTF948 or DTF948O, Request for Information (RFI). Check for corrected reports and see if there is any reason for the different wage totals. • Fill out the enclosed questionnaire and return it within 45 days. Check for corrected reports and see if there is any reason for the different wage totals.