I have a client who received several years of LTD payments. Taxable income and we claimed the W2 wages (box 1) on his returns. Social Security ended up paying a lump sum of back disability payments covering 4 years,  and the LTD insurance company took the entire amount as repayment. 

How do I deal with this on tax return. If I just enter the social security form as is, the entire distribution will be taxed. Same is true if I had spread the amounts over the last 4 years. 

However he already paid taxes on the LTD paid (which has now been paid back). So it is double taxation if he paid LTD payout taxes, and pays SocSecurity taxes. I am at a loss and cannot get through to the IRS. thought maybe you nice people can help

Is there a way to claim the funds were already taxed in previous tax returns on this current 2019 return? Amend old returns?