Why are you overpaid? Did you earn over the exempt amount (around $15,000) annual earnings test? Sounds like you probably did since you worked full time through 65 1/2 but were paid retirement benefits at the same time. Since you were overpaid for age 62-age 65, you are not going to be paid for the increase in benefits.

Probably best if you file a Request for Reconsideration on a notice that you disagree with and explain why you think the numbers are wrong. But I don't think you are due any additional money for the months that you were actually overpaid.