i-864 adding social security to total income

[MdFS 0]

after the interview i was informed to submit new joint sponsor, because on tax form the total income (taxable) was 23000$ which is less than 125% of poverty for household of 3.
unfortunately it was the only taxable part of the income, 20000$  (taxable from 1099R) and 3000 ( taxable from social security benefits), and did not include the nontaxable 26000$ of social security benefit.
I was given 221g, new joint sponsor required. i consulted a lawyer and he prepared a revised i-864 for me with total income 46000$ and explanation letter defining both taxable and non-taxable income and highlighted to consider social security benefit as well.
after submitting those  document, Embassy responded  on tax form that  "only total income counted towards affidavit of support. joint sponsor required" (they are non counting social security benefit of 26000$)
and for revised i-846 of same joint sponsor with corrected income, embassy commented that " Identical document submitted, please submit new joint sponsor)

can anyone please guide me, what is going on, why are they  not accepting social security benefit income as part of total income regardless of explanation provided. and what can i do for it.
i have read similar cases, who did the same and they accepted that.