Disney usually sends out a letter about a month prior to expiration. Most folks get it, some never do. Call 407-560-PASS and explain to them what happened. They may be able to still put your renewal through for you.
Ours expired 8/26..I let them expire b/c we were going on FTP...no annual pass rates available. Well rates came out and I called after labor day to get the annual pass rate and was talking to the CM about being to late to renew and he said "oh no your not!" and it was over 30 days since it expired & I renewed w/ a DC discount..so call!