still can't remove popcorn ceiling - what am i doing wrong?

Nine times out of ten it's been painted over. Bare popcorn soaks up water and scrapes off like wet porridge, but a coat of paint seals it so the water just beads and runs off. Try a small patch: spray it with warm water and a drop of washing up liquid from a garden sprayer, wait 15 minutes, then scrape with a wide blade. If it stays hard, it's painted, and you're looking at a lot more soaking and scoring or just skimming over it instead. Before any of that though, if the house is older (pre-80s in the US, pre-2000 in the UK) get a sample tested for asbestos. Cheap to do and you really don't want to find out afterwards.