John 6:36

ἀλλ' εἶπον ὑμῖν ὅτι καὶ ἑωράκατέ καὶ οὐ πιστεύετε.

Rough Word-by-word:
but I said to you all that also you all have seen and not you all believe.

Smooth Translation:
but I said to you that you also have seen and you do not believe.

or

but I said [this] to you because you also have seen and do not believe.

Notes:
They have seen - note the perfect and yet they are not now believing - note the present.
I'm reminded of those at the end of John 9 that said they "saw."

ἀλλ' strong adversative conjunction "but"

εἶπον verb aorist active indicative 1st singular from λέγω (I say) "I said"

ὑμῖν pronoun dative 2nd plural "to you all"

ὅτι conjunction "that, because"

καὶ conjunction "also" (adverbial use)

ἑωράκατέ verb perfect active indicative 2nd plural from ὁράω (I see) "you all have seen"

καὶ conjunction "and"

οὐ adverb of negation "not"

πιστεύετε verb present active indicative 2nd plural from πιστεύω (I believe) "you all believe"