A twin bed to a king bed may be a substantial upgrade at many hotels, spanning several categories. An "standard" upgrade for someone that booked a twin bed may be a twin bed room with a better view/location. When booking hotels with the hope / expectation of an upgrade, one must get a good sense of the various categories, roles, etc.

Perhaps the customer service wasn't as good as hoped but an upgrade to a king room may not be required per Marriott rules