Yeah, it's not hacking. Those teams are just geared better which is why you're getting those responses from support, unfortunately. Without seeing your gear/team and some of the instances where you're losing (perhaps going against a Leorius, Skullcrown, champs with Swift Parry, etc.) it's really tough to say where you're going wrong or what the problem is. Can you post your roster, gearing, masteries? Thanks.

There is no known damage hack in arena. You just lost, because your opponents did understand how arena works and you don't.

This pic from my most recent fight in Tag arena just provs that team power doesn't matter.

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Match no. 1 I lost with a high team power team vs. a team with much lower power. My own fault, I should have changed my teams no. 1 and 2, Uugo with her block buffs is a huntress collecting lions skulls. Match no. 3 my low power team defeated his high power team

 If you lose vs. a team of 2 champs, that's in no way of proof for hacking.

But, indeed there are speed hacks, making PvE tournament competitions quite unfair. Plarium says, they have a cheat protection, and some combinations like Taurus + Zavia or Mausoleum Mage + Seer with Prince Kymar to reset their skills can kill dungeon waves within seconds, so it's hard to say if other players in your tournament group are speed hackers or if they just have a team fitting perfect for this dungeon.