Bit confused by Delta at the moment. I'm on a Delta Marketed but KLM operated flight in B class. I reached out to attempt mileage upgrade award per the website

• For KLM-operated flights, Mileage Upgrade Awards are available from Economy to Business, and may be used on the following paid fare classes: Y, B, or M.

But they are telling me now that B and M are only eligible if its both marketed and operated by KLM and since my flight is only operated by KLM with a Delta flight number, that they can only upgrade me if I'm in Y class.