Well, I'm not a Roman Catholic, I'm Orthodox.

First off about calling no man father, Jesus isn't saying we can't call people "teacher" or "father", that's silly. If Jesus were speaking strictly literal, we couldn't call our own biological fathers, "father", or people who are teachers, "teacher."

Paul would also be guilty of this if Jesus were speaking strictly literal, as he called Timothy and others his son, and called himself a teacher. Jesus is addressing the pride and boastfulness of the Pharisees who seek to be called great titles.

Secondly, we don't deny that Jesus is the mediator. We pray to the Angels differently than we pray to God, they pray for us or offer our prayers to God. So we're not denying Christ as the one mediator by asking for the prayers and help of Angels.