You may have ticked the box to have a Social Security Number assigned and sent to you, but historically, it only has worked about 50% of the time. If you do not have a SSN letter by October 15th, then head to your local Social Security Office to enquire. Don't go before the 14 days, as it does take some time to process the request, as the SS Administration is a separate entity from USCIS. If the officer who processed you through at your Point of Entry did not tick the box on his or her screen, then the request will not be generated. Happened to us, even though we specifically asked the officer about it.
You were not nor will you be charged for a Social Security Number.
Sukie in NY