Need colorful synonym for "dumbfounded" or "baffled"

I need a colorful synonym for "dumbfounded" or "baffled". It's on the tip of my tongue. It's a multi-syllable word.

Context: "I checked with xxx and yyy (experts). They were both as dumbfounded as I was by So-and-So's letter, saying they've never heard of a request for m being treated as n.

(An administrator had confused two completely different rights and their legal underpinnings.)

Hornswaggled is the closest so far. (The dictionary I consulted said hornswoggled, and it gave a very different definition.) But I think there's something that's just one notch more mainstream than that, only that I can't remember it.

I'm seeing some suggestions that don't mean the same thing as dumbfounded/baffled. Here's the definition for dumbfounded: "to make speechless with amazement; astonish."

Here's a made-up similar context:

I double-checked with my botany professor. She was as ____________ as I was by your lecture notes, saying she's never seen a maple confused with an oak before.

EDIT: Guys, "hornswaggled/hornswoggled" is colorful. Astonished (for example) is not colorful.

Astonished, astounded, flabbergasted, flummoxed, gobsmacked, speechless, stupefied.

Flabbergasted is the best example of a multi-syllable synonym that comes to mind.

Consider,

discombobulated

to discombobulate: to confuse; befuddle AHD

obfusticated

: Dial. obfuscated; confused; bewildered M-W

confusticated

confusticate: Sl. to confuse or perplex; bewilder Random House

metagrabolized/metagrobolized

: totally perplexed and mixed up WordNet by Farlex

addlepated

: being mixed up : confused M-W

bamboozled

I double-checked with my botany professor. She was as bamboozled as I was by your lecture notes, saying she's never seen a maple confused with an oak before.

• 2. to perplex; mystify; confound.
     Synonyms: befog, bewilder, puzzle, baffle, dumbfound.

Dictionary.com explains further

Bamboozle is one of those words that has been confounding etymologists for centuries. [...] By 1712, it had acquired the sense “to perplex; mystify.” It is not known for certain, but this sense might have emerged under the influence of the Scottish word bumbaze (or bombaze), meaning “to confuse,” similar in both sound and meaning. Given the befuddling qualities of alcohol, it's not too surprising to find that, in the 1800's, bamboozle showed up on college campuses as a slang term for “drunk.”