I am a Diamond Ambassador. I called Diamond member phone line today to request using a CSU with my upcoming stay in IC Melbourne in 14 days in a Classic Room with award stay. They said they had to check the suite upgrade inventory and can only provide me a premium room or a Junior Suite at best despite there are a lot of availability for Double Classic Family Room and Signature Suite (which is their Standard Suite) on sale. I know the agent was trying her best so I don't blame her.

She told me that CSU can only provide 1-category upgrade, which would be from Classic room to Premium Room.

This is rather useless for me because Ambassador elite guaranteed a 1-category upgrade and it's not stackable with CSU. But I thought the policy for CSU is to guarantee a standard suite that is available at the time at the request. What should I do? HUAC?