The usual mistake is to calculate the probability to get one after 100 runs (equivalent to 500 with 1.5% chance). One should calculate the chance to get at least one, that means add the chance to get 2,3…500.
With 30 runs, I calculated around 90% chances to get at least one provided RNG in the game is true RNG (not so sure about that).
I finally got my first after 75 Tormented Boss runs.