Heaven refers to the New Earth and New Heaven in the Bible. It is referred to as the Temple in Revelation, that is, the Most Holy Place in the heavenly Tabernacle. The second curtain to this place is opened after Jesus. Jesus is currently the only one (symbolically ever as a human) entered.
Saints such as Elijah and Enoch are supposed to be in another location called Abraham's Bosom (in the Third Heaven) to continue to bear witnesses for God.
Heaven refers to the sky above, the space above our earth, and the throne of God. That is why Paul speaks of a vision of being caught up into the "third heaven" 2 Corinthians 12:2 when he speaks of visions from the Lord. That's also why it says the stars are in heaven and that birds fly in the heaven above. When Jesus says that "no man has ascended to heaven" he is obviously speaking of the third heaven, which excludes "Enoch and Elijah" being in heaven in any form (as they certainly aren't on the moon or in the clouds.)
Further, if we needed any more verification on this, Paul plainly says that Enoch died and received not the promises, and that his hope is in a better resurrection. It's in Hebrews 11. We have a whole massive chapter in 1 Corinthians telling us that the hope of the Christian is the resurrection of the dead, and that IS Paul's definition of the gospel. We have Jesus telling us that no man has ascended to heaven. And now we have a huge long passage in Hebrews telling us that
the perished saints have not yet been rewarded.
Heb 11:5, 13 KJV
(5)
By faith Enoch was translated that he should not see death; and was not found, because God had translated him: for before his translation he had this testimony, that he pleased God.
(13) T
hese all died in faith, not having received the promises, but having seen them afar off, and were persuaded of them, and embraced them, and confessed that they were strangers and pilgrims on the earth.
Heb 11:32-40 KJV
(32)
And what shall I more say? for the time would fail me to tell of Gedeon, and of Barak, and of Samson, and of Jephthae; of David also, and Samuel, and of the prophets:
(33) Who through faith subdued kingdoms, wrought righteousness, obtained promises, stopped the mouths of lions,
(34) Quenched the violence of fire, escaped the edge of the sword, out of weakness were made strong, waxed valiant in fight, turned to flight the armies of the aliens.
(35) Women received their dead raised to life again: and others were tortured, not accepting deliverance;
that they might obtain a better resurrection:
(36) And others had trial of cruel mockings and scourgings, yea, moreover of bonds and imprisonment:
(37) They were stoned, they were sawn asunder, were tempted, were slain with the sword: they wandered about in sheepskins and goatskins; being destitute, afflicted, tormented;
(38) (Of whom the world was not worthy, ) they wandered in deserts, and in mountains, and in dens and caves of the earth.
(39)
And these all, having obtained a good report through faith, received not the promise:
(40) God having provided some better thing for us,
that they without us should not be made perfect.
... and he lists Enoch among those perished saints. Tell me, if saints were in heaven, why do we not have a chapter telling us so, and how come we have so many places in the bible that contradict such a teaching?
He says clearly, "
that they without us should not be made perfect." That means that the perfection he speaks of to the Corinthians happens all at once for everyone. At the resurrection of the dead. Without which we cannot inherit the kingdom of God.