Funny, Paul nor any of the other NT writers ever appealed to Abraham or Elijah or anyone else except God.
Early Christians did, though, in all the churches founded by Apostles. It’s part of the Apostolic teaching. St. Paul told St. Timothy that all of Scripture is useful for instruction, and the Septuagint -—their Scripture -—made it clear to them that those in heaven prayed for them.
As well, St Paul exhorted his converts frequently to hold fast to the traditions (not any-old-traditions, but Apostolic Traditions -— we’d give them a capital “T”) and to follow their oral teaching, as well as their practical example. As you know, the Church had liturgies (approved forms of public prayer), creeds, catechisms like the Didache, and bishops’ homilies to draw upon, for many generations before they had winnowed out all the extant writings and approved the canon of the New Testament.
So it was obvious to them that they should go the successors of their Apostolic founders for guidance. Logically and chronologically, the practice of the Church preceded the canonization of the texts.
They knew, too, that Jesus had promised this authority to the Church, against which the gates of hell would not prevail.