You attacked 25 times a lineup, with the same offensive lineup. ?
With all do respect, that is fool, like hitting your self against the wall thinking you are going to take it down.
Come on, just after the 1st fight, look at the "I"(nformation) of the battle, where it shows all the stats, specially the runes in each heroe.
Compare your stats.
Change your runes.
Change the offensive lineups.
And if you can't beat him, just attack the next one (2nd place), and so on...