Ok ... so you sent in only the 1040X & the 1099-B from the broker ??? If so the IRS is rightly confused since you should have also mailed in the Sch D & form(s) 8949 showing the sales.
Now ... if all the sales are COVERED then just stop ... you do not need to amend the return. Keep the records just in case they send a notice later (doubtful).
However, if any of the were NOT COVERED then mailing in the 1040X again with the Sch D & 8949 would be the correct thing to do.
