Many saints have said this. It is undoubtedly true, that to disdain the intercession of Mary is to close off the hope of salvation, since it is the same as disdaining the bestowal of the grace of God. The fifteenth anathema of the Second Council of Nicea (Ecumenical 7) reads:
(15) If anyone shall not confess the holy ever-virgin Mary, truly and properly the Mother of God, to be higher than every creature whether visible or invisible, and does not with sincere faith seek her intercessions as of one having confidence in her access to our God, since she bare him, let him be anathema!
Also:
(17) If anyone denies the profit of the invocation of Saints, let him be anathema!
The priest you mention was quite right.