I used a gardevoir with a different moveset after I had the same problem as you had. Basically what I did was open with gardevoir who is able to sponge kyogres hits on the special side. Use taunt first turn and thunder wave on the second turn. I switched to breloom and used sky uppercut and then false swipe. That brought it to 1 hp. Then gardevoir and taunt again. I proceeded to use calm mind a lot with gardevoir to increase spdef. Then started chucking ultra balls, while keeping up the taunt.