Destroyed how, you can't handle his shields? Do more damage, get Shieldbreaker mastery, or just go faster and do most of the damage before he even takes a turn... if the problem is his sleep debuff, higher resistance on your champs could help, or again just being faster. Zelotah is a good champ for dungeon progress but he's not that impressive in arena, other than his aura - but if they're using a resistance aura, they don't have a speed aura and you should be able to outspeed them. 

No, it's because of the heals which I can't handle + the shields I fail. I have Samar whose A3 is to damage everyone and steal their buffs, but for some reason it always fails with Zelotah.

Buff stealing needs accuracy and can be prevented with resistance. Your Samar needs more accuracy.

Can you show us your champions? perhaps we can point out potential comps by which you can counter such buffs

thank you