Ok we differ on how we read that scripture.
Jesus says this as you have quoted:
Joh 3:13 And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.
And it is in this context:
Joh 3:11 Verily, verily, I say unto thee, We speak that we do know, and testify that we have seen; and ye receive not our witness.
Joh 3:12 If I have told you earthly things, and ye believe not, how shall ye believe, if I tell you of heavenly things?
1st bringing or testifying of heavenly things. So no one has ascended to heaven except Jesus who has come down to testify of heaven. Only Jesus has done this, even though both Moses and Elijah had come down they did not testify to the world of heavenly things as Jesus did.
Second:
Joh 3:13 And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.
Joh 3:14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up:
Joh 3:15 That whosoever believeth in him should not perish, but have eternal life.
It is in the context of righteousness by faith through Jesus. I believe Jesus is using an idiomatic phrase by borrowing imagery from here:
Deu 30:12 It is not in heaven, that thou shouldest say, Who shall go up for us to heaven, and bring it unto us, that we may hear it, and do it?
Jesus is our righteousness which we have by faith in Him, he came down that we need not go to heaven in order to find or have it.
Thus I don't think Jesus is saying no one else has ever gone to heaven as we are told Elijah did. But rather that no one else has come form heaven who testifies of heaven and also brings righteousness by faith.
You may not agree but I find this to be in harmony with other texts and fits the contextual arrangement. Jesus is speaking to a teacher of the law who would have made the connections.
That is why after alluding to Deut Jesus immediately alludes to Numbers 21 about Moses and righteousness by faith. It is contextually and logically compliant.