ssdi lump payback

my wife has a disability policy she has been collecting since 2020. she applied for ssdi as required buy the insurance company. she was approved in 2023 and received a large backpay check from ssdi. her policy required us to repay that lump sum from ssdi back to insurance company. the insurance company and accountant said this large payment was not taxable as it was a repayment. now the the irs says we owe taxes on 70k in money we didnt get to keep. anyone have any irs info that states repayments like this are or are not taxable?