I have that question also. I was approved for SSDI is 2019. I have been off work since Aug 2017 and approved for SSDI in May of 2019.  I have filed both my 2018 and 2019 tax returns. After I got approved, my Social Security sent me a huge check, but was immediately withdrawn from my bank account by my LTD insurance company. I did not touch any of that. I recently received a 1099 form from Social Security stating that my Net Benefits for 2020 is $63,062. Down at the bottom it shows that this amount includes $22,968 paid in 2020 for 2019 and $16,758 paid in 2020 for 2018. I didn't get any of this money in 2020. I am not sure if they are referring to my lump sum back payment I received in May of 2019. 

I also received a letter from my LTD insurance company saying that I may have the opportunity for an income tax offset. 

I don't know how I would even pay something like this. If you found out an answer, would you please be so kind to share with me?  Thank you.