Last year my W2 said I earned $29,235 (box 3) and $3,636 was withheld for Social Security (box 4). I was informed by FreeTaxUSA that my [former] employer overpaid/withheld and owed me $1818. Now the employer says that he made a mistake on box 4 on the W2. He should've stated $1818 (just the portion he withheld from my wages). If he amends the W2, do I have to re-do last year's taxes? Moreover, who owes money - me?