Hi and welcome. It can take a bit of time for the ammonia to start dropping but it usually does drop in 2-3 weeks. Let's just check a few things:
1. what temperature is the tank? the warmer the temp, the more inviting for bacteria. The recommended temp is about 86 if you can get it there
2. Does the ammonia bottle foam when you shake it? If it foams, it may have surfectants or other things that may inhibit the bacteria from forming
3. Is there surface agitation in the water created by the water from the filter splashing the surface or an air stone? Bacteria like oxygen
4. What test kit are you using? if you're using strips, they aren't very accurate and it's possible they are giving false readings.
5. Also be sure you only dosed to about 4, no more than 5, otherwise it can keep the cycle from happening
6. Did you use dechlorinator when filling the tank? What brand? Be sure on the bottle it says it dexotifies heavy metals, chlorine and chloramines
7. You might want to get some seeded filter material.
This site sells "active" seeded sponge filters from their fish tanks which can help greatly. Just be sure it says "active" next to it otherwise you're just buying a plain filter.
Good luck and let us know if we can help further.