Ok ... that is a real tangled mess ... if the IRS accepted the efiled return with the new SS# then the original mailed in return may never be processed at all. Please seek local professional assistance either at a local income tax office or with a tax attorney/enrolled agent.
What you will need to do is file a form 14039 to get an IP PIN for the child so no one else can use their SS# on a return without the PIN. This should stop the bio dad in the future.
