I'd keep pulling on the emergency cord. Only give that option up if you break the line.
How I remember getting mine open : remove the rear seat, have the left rear door open all the way, stand on the other side of the door so that your next to the left front door, pull from that point. The plastic ring is hard to pull on so I pulled a rag through it so I had something more to grip. Then pull slow and as hard as you can. Vala, open says you.
Good luck.