Stand as close to the wall as you can get, save and re-load. Also, you may be able to find a gap in the wall to get back trough.

Otherwise; Teleporting Anywhere, via hex editor

Do you have one or both teleporter stones, or is this Iona's dungeon you are talking about? If you do have them, a more elaborate way to get out (but which does not require a hex editor) is described in;
FIX for the Missing Catacombs Portal