iCloud storage for Messages is not in sync with devices

Hi Community,

I receive "iCloud storage full" notifications almost daily, and I want to avoid paying for iCloud.

According to iCloud.com, Messages is using 4.7GB:

I have two MacBooks (work & personal) and an iPhone. All three devices are logged into iCloud and have the settings enabled to sync Messages with iCloud. All three devices are set to a 30 day retention period, and I confirmed that none of the devices have old messages on them. I have no other devices on my iCloud account using Messages. All of these settings were updated several months ago in ~February. I have also tried the "Sync Now" button in iMessage on OSX, but it always seems to hang indefinitely.

According to my iPhone, my actual Messages storage is 429MB:

Apple continues to suggest that I need to buy iCloud, but what I really want to do is delete all the Messages in iCloud and re-sync.

Is this possible?

Thanks,

David