Free of charge XL seat on SFO-TXL for award flight for OW Sapphire
 

I booked economy award flight SFO-TXL, and as OW Sapphire, I expected I could select any seat free of charge on the AB website, but I couldn't.

So, I contacted customer service, and (after one week of waiting) I got a response from them: 'Please be informed that according to your frequent flyer status, the seats can be assign free of charge only in category B. ( which is the middle section, where are 4 seats )"

I believe OW Sapphire is equal to AB Gold, which would give me access to XL seat free of charge.

Who is right in this case?

AB Gold may be equal to OW Sapphire but that doesn't mean ALL OW Sapphires get the same benefits as AB Golds. Some benefits are offered on the OW level - lounge access, priority checkin, standy, boarding, etc. but access to seats on the plane is not one of them. Individual FF programs are required to offer the OW benefits but they can offer more to their members - just because you have OW Sapphire status with another program that happens to be equal to AB Gold, doesn't mean you'll be conferred the same benefits as AB Golds.

The same practice is used by other airlines. For instance LH only extends benefits to eurowings pax who hold MM status (not to *A status holders).