Hiya Mr.Fish and welcome to Aquariumadvice
Ammonium chloride SHOULD work. Since its not, try picking up a bottle of ammonia from the supermarket (make sure its PLAIN ammonia, not sudsy or one with any sort of additives); add around 3-5 drops per 10g. Maybe that will make a difference.
What else are you adding to the tank? What are you using to treat the water, or are you adding anything at all?
Are you using any bacterial starter (Bio-Spira, Cycle, squeezings/gravel from a mature tank, etc).
Have you tested for nitrites, nitrates yet? If so, are there any readings?
And even tho you've tried a coupla diff tests, bring a sample to a lfs
and have them check too. They may give you some flack for doing a fishless cycle (many lfs
have a prob with it; means they aren't selling fish yet I guess *grin*), but don't let it bug you.