Showdown aka spend a million coins

Why is it when I select an opponent before i spend 2500, 5000, and 12,500, even 25,000 coins it says opponent unavailable, while in my defense log the same opponents have beat me on average 3-4 times. I shouldn't have to spend 45,000 coins on each turn. Can the system that determines your opponent be adjusted to help out their clientele on this because literally spending a million coins to be able to attack is ridiculous, and why does it give me the option, then deny the same option they give me...