Xbox 360 Theives Guild Quest Help?

[Nathanial]

I accidently went through a load door when i was supposed to follow Brynolf and now i can't talk to mercer frey which was supposed to happen (i played it with a different character). I want to do the theives Guild questline with my favorite charachter which is the Arch-Mage, Beaten Alduin, Nearing the end of The Dark Brotherhood questline. This glitch occured a while ago with this character so reloading doesn't work i tried it at the time. Searching and trying solutions ever since so i need some help if someone can figure out the glitch.

 

[Miles Verne]

have you got a save point prior to the quest that you can load? That seems like a very weird glitch, espcially on a console. Ive never had any issues with the thieves guild quest line and ive completed it at least 3 times. Odd