@Rostonllc1, while it is true that an IRS 12C letter may be asking for form 8962, in this case what the Original Poster (OP) indicated was that the letter was asking for proof of federal tax withholding. The withholding could be on form W-2 or W-2G or any of a number of 1099s or, as in this case, SSA-1099. If the IRS had wanted form 8962, the letter would have explicitly said so.
@dane1234, I presume that this issue has long been dealt with (and successfully I hope), but based on what you have written, it would seem to me that either the Social Security Administration (SSA) failed to send a copy of your SSA-1099 to the IRS or sent it with a different amount for withholding. Yes, the SSA does copy the IRS on the SSA-1099 as a matter of course.
I presume that you sent the copy of the SSA-1099, and that you and the IRS have communicated and straightened out the confusion.
