No one has ascended to heaven but He who came down from heaven, that is, the Son of Man who is in heaven. John 3:13
Of course John 3:13 was true at the time, before He was crucified, and was in the heart of the earth.
The Old Testament saints were in the heart of the earth called Abraham’s bosom, which was also called Paradise.
Jesus said to the thief on the cross, this day you will be with Me in paradise. Jesus didn’t ascend until the third day.
Jesus taught us about life after death for the Old Testament saint.
19 “There was a certain rich man who was clothed in purple and fine linen and fared sumptuously every day. 20 But there was a certain beggar named Lazarus, full of sores, who was laid at his gate, 21 desiring to be fed with the crumbs which fell[d] from the rich man’s table. Moreover the dogs came and licked his sores. 22 So it was that the beggar died, and was carried by the angels to Abraham’s bosom. The rich man also died and was buried. 23 And being in torments in Hades, he lifted up his eyes and saw Abraham afar off, and Lazarus in his bosom.
24 “Then he cried and said, ‘Father Abraham, have mercy on me, and send Lazarus that he may dip the tip of his finger in water and cool my tongue; for I am tormented in this flame.’ 25 But Abraham said, ‘Son, remember that in your lifetime you received your good things, and likewise Lazarus evil things; but now he is comforted and you are tormented. 26 And besides all this, between us and you there is a great gulf fixed, so that those who want to pass from here to you cannot, nor can those from there pass to us.’
27 “Then he said, ‘I beg you therefore, father, that you would send him to my father’s house, 28 for I have five brothers, that he may testify to them, lest they also come to this place of torment.’ 29 Abraham said to him, ‘They have Moses and the prophets; let them hear them.’ 30 And he said, ‘No, father Abraham; but if one goes to them from the dead, they will repent.’ 31 But he said to him, ‘If they do not hear Moses and the prophets, neither will they be persuaded though one rise from the dead. Luke 16:19-31
Notice that Abraham nor the rich man nor Lazarus was “asleep” in a grave in the ground.
Furthermore, other things changed after He was crucified.
51 Then, behold, the veil of the temple was torn in two from top to bottom; and the earth quaked, and the rocks were split, 52 and the graves were opened; and many bodies of the saints who had fallen asleep were raised; 53 and coming out of the graves after His resurrection, they went into the holy city and appeared to many. Matthew 27:51-53
Jesus spoke the truth in John 3:13 as well as everywhere else.
Paul did also.
There are saints who have died in heaven and they will return with Him when He comes.
JLB