Carcer and I can independently verify that all your math checks out.
That said, take a deep breath. I doubt this question was prompted by your lack of faith in your own math and reading skills, but instead by your DM's insistence that this encounter wasn't deadly, and this much bold formatting and all-caps in a question (prior to style edits at least) makes it pretty clear that personal feelings are running hot (and probably being hurt) over this issue. If the game is causing you that much stress, maybe it's time for a break, or for a different activity - or for just walking away. No game is preferable to a game prompting this kind of emotional response.
So why are they saying it's not a deadly encounter? I'm not your DM, so I don't have direct access to their thought processes and reasoning, but if I had to guess?
Maybe they don't realize they need to add the additional difficulty multiplier for groups of monsters, as this is something that causes some confusion in 5E. Under this math, the encounter would incorrectly show as medium.
Maybe, and this is what I believe is most likely, you're not talking about the same thing when you say "deadly encounter". They could be using "deadly" to refer to the encounter in plain English - like "trivial" or "effortless" or "frustrating" - while you use it to describe this very specific 5E concept of encounter difficulty. Few things are more frustrating than being separated by a common language like this.
Maybe the oozes were at some disadvantage: surprised, distant enough for your ranged folk to get a licking in before they closed the distance, or something else specific to the encounter that only the DM knew about. Per the DMG, a disadvantage like this drops the encounter one step from deadly to hard.
Maybe the encounter was the first, last, or only encounter in the adventuring day. All of these affect the perceived difficulty of the encounter, despite having identical XP values and theoretically taking up the same fraction of the party’s resources (hp, hit dice, spell slots, etc) per adventuring day. Earlier encounters give you more flexibility in matching the right resource to the encounter (such as using your spell slots to get around damage resistances that would prolong hp-draining melee combat) and more assurance that if things do go pear-shaped you can still handle it, and so they feel easier even if they take more out of the party. The later an encounter gets, though, the less these apply. If you lose almost all your resources to an encounter, it still feels like you made it by the skin of your teeth, even if it was only a small fraction of your adventuring day’s resources. Spending half your Hit Dice and all your spell slots is still going to feel less tense than spending a single hit die, if its your very last one.
If you haven't already done so, I would recommend just talking to them to see if it's any of these. And when you do, give them the chance to explain; they may ultimately be in the right here.