Correction in GSTR1 of FY19-20

We have mistakenly shown the sales Bill to 'Mr.A's' GSTIN, while it was supposed to be shown on 'Mr.B's' GSTIN. For the entire year FY.19-20.

Now after 2 years, 'Mr. B' claims that he has not received the Bills ITC and has stopped our payment of the equal amount of GST ITC Tax.
he demands the Bills ITC. which is not possible. as the amendment option is also lapsed.

any good, effective and immediate solution?

Kindly, help urgently.