You may call Gold Elite line, then (after choosing option 4) tell CSR that you want to talk to CO.COM support desk because you couldn't redeem coupons on-line. (Elite line's CSR will still charge you booking fee.)

One additional note, those coupons/certificates w/o PIN code need to be mailed-in to Continental's Houston address (PO Box) after redemption.
Support desk rep will tell you how to do it. eTicket will not be issued until they receive mailed coupons.