"Jesus is described as having “ascended into heaven” and...

"Jesus is described as having “ascended into heaven” and “descended from heaven” in John 3:13 (ESV)."

I quote the above, not to address whether there is heaven, but this verse is Not describing a pre-existing Jesus coming down, it is a prophesy, a future event, a heavenly event that is yet to take place, which Jesus is describing.

John 3 - If I have told you earthly things, and ye believe not, how shall ye believe,if I tell you of heavenly things?
Future heavenly event following;
And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.
Now he explains what he mean here, interprets it, elaborates;
And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up: = Future heavenly event, yet to happen.

He rose from the dead and said touch me not, as I have not yet ascended to the Father etc.
He goes up to the Father, heaven, came down from heaven for 40 days and goes back to heaven, just as described in the verse you quote.

John 17:17 - Sanctify them through thy truth: thy word is truth.