Underground pass help please

[Cwmbran]

Ok, i have got to the part where you have to go into the temple to face Iban, it says only followers of zammorak can enter so I kill some Iban disciples and put on the robes of zammorak and I go to enter the temple, I get the same message "The door refuses to open...
Only followers of zammorak may enter"

Have I missed anything out?

+Rep for anyone who helps.
Thanks.

EDIT:

Don't worry I found out why I could not get in.