When you empty a fire extinguisher that you've already collected, does it puff a single time, or does it shoot fire? If it puffs a single time, then you are still missing some extinguishers.

On the level select, when you hover over each chapter, you will see icons indicating whether or not you've collected everything in that chapter. A grayed-out icon means there are still collectibles of that type in that chapter to find. Pure white means you've found them all. An icon with a red slash across it means there are no collectibles of that type in the chapter.

If your extinguishers do indeed shoot fire when clicked, but you don't have the achievement, you can try resetting achievements in-game and collecting them all again. Go to Options -> Achievements on the main menu and click "RESET ACHIEVEMENTS AND TRACKED ITEMS" at the bottom-right.