Have you tried tightening the switch retaining ring? It is located under the black disk, with openings near where the two cut-outs are in the black disk. A good pair of fine metal tweezers should do the job. Just insert the tips into the metal divots on the ring, and turn clockwise to tighten. Snap-ring pliers would also work, although few people have those.I've got a problem with mine. The gold connector in the tail cap has come loose and now it's not working rendering this useless.
It's not uncommon to have these rings loosen up with time, eventually rendering the light inoperable. Usually, this simple fix is all that is required. In fact, I'm surprised they didn't recommend that before sending you a replacement part.