"cleaned it out really good" might be the problem. Did you clean every single thing in the tank and add new water? That being the case, you're going to need to recycle it. You would have been better off leaving things as they were after you removed the fish, and for whatever you removed them for, worked from there. Basically, what I'm trying to say is that cleaning the tank completely makes the tank as if there were nothing ever in it before. So, you need to start from scratch. I'm still very puzzled as to how the ammonia smell came from the tank in the first place since you cleaned everything out as said, since ammonia doesn't just show up one day. It needs to be an introduced source. Since there are no fish in the tank, I'm frazzled. For now, you should probably try the ammonia/nitrate/nitrite test kits and buy the drops, not the strips. The strips aren't as reliable and I have found their shelf-life staggering (for lack of a better word).
As far as adding the ammonia bag instead of testing, I wouldn't have suggested an ammonia bag being placed in the tank, I would have suggested daily/weekly water changes according to your test kit but you didn't get the kit.... however, I still would have said don't waste your money on the bag since you are in the start of a cycle somehow so water changes are a must to get things stabilized and that's all it would've taken. The bag merely takes care of the problem short term when you've got something weird going on that needs to be addressed. It's kinda like spraying air-freshener in a smokey room. You can cover the smell, but you can't get rid of the source without a cleaning.
(sorry for the ramble)