I can sympathize. When I played a Wizard (Illusionist) in one game, the GM basically ignored my illusions -- even though I replicated monsters encountered earlier in the game. I had to call him on his bias when Orc warriors acted as if the illusionary Hill Giant wasn't even there. How a GM adjudicates illusions tells you a lot about his/her bias, understanding of rules, and maturity.
I guess you need to use non-divination based methods to find the opponent, such as Deathwatch, Blindsight, Scent, Perception, Glitterdust, Invisibility Purge, Dispel Magic, Antimagic Field/Ray, etc.