As a counterpoint, the last time I spoke to JAL's US call center, the service was nothing short of excellent. The wait time was atrocious (I called during the east coast lunch period), but once I got a representative on the line they very quickly helped me with my issue.
In your case though, it seems like your problem is with the CX agent who told you they couldn't help (though CX's terms may not offer any flexibility in the case of an aircraft change).