How many times have you challenged the battle tower before you beat 50 trainers? 
 
I have beat 550 trainers in the tower but still have not beat 50(highest i have gone is 43)  in a row (level 50) WHATS WRONG WITH ME?!? 
But why i haven't beat it is the stupid part. I have a Swampert, Latios, and Metagross all at level 50, all stats and HP beefed up, all holding items that make them stronger, but then a really cheap A.I. trainer uses "double Team" like ten times in a row making him untouchable while he slowly diminishes my HP with crappy little harmless attacks until I'm beat. This has happened to me at least 5 times in the past, and just recently new nightmares have appeared: "yawn, sing, grass whistle". my last recent try a slacking used yawn on each of my pokemon and defeated me! so much shame!!