I gave up and sent my 8962 priority mail so at least I had a tracking number and it still took several days before it was delivered because I got text messages that they were unable to drop off for several days.
I got a letter from the IRS about needing the form and inside that envelope was a self-addressed envelope that I used. My letter had an address: IRS, Stop 6120, Kansas City, MO 64999. I don't know if that applies to everyone because it could go by region. I will say to definitely make a copy of all of your docs including the IRS letter to keep as a backup.
