“Number the bishops from the See of Peter itself. And in that order of Fathers see who has succeeded whom. That is the rock against which the gates of hell do not prevail” Augustine, Psalm against the Party of Donatus, 18 (A.D. 393).
“I am held in the communion of the Catholic Church by…and by the succession of bishops from the very seat of Peter, to whom the Lord, after His resurrection commended His sheep to be fed up to the present episcopate.” Augustine, Against the Letter of Mani, 5 (A.D. 395).
“Carthage was also near the countries over the sea, and distinguished by illustrious renown, so that it had a bishop of more than ordinary influence, who could afford to disregard a number of conspiring enemies because he saw himself joined by letters of communion to the Roman Church, in which the supremacy of an apostolic chair has always flourished.” Augustine, To Glorius et.al, Epistle 43:7 (A.D. 397).
“And since these heretics were trying to bring the Apostolic See round their view, African councils of holy bishops also did their best to persuade the holy Pope of the city (first the venerable Innocent, and afterwards his successor Zosimus) that this heresy was to be abhorred and condemned by Catholic faith. And these bishops so great a See successively branded them, and cut them off from the members of the Church, giving letters to the African Churches in the West, and to the Churches of the East, and declared that they were to be anathematised and avoided by all Catholics. The judgment pronounced upon them by the Catholic Church of God was heard and followed also by the most pious Emperor Ho they had wandered, and are yet returning, as the truth of the right faith becomes known against this detestable error.” Possidius, Life of Augustine, 18 (A.D. 437).
Also, the last one you quoted, from his retractation, does not help your case. He leaves the question about the Rock undecided.
How strange...