Greetings, I have an upcoming flight in J from LHR to JFK that I booked on a partner ticket. I checked the seatmap on expertflyer and on BA's own website when I booked and it appeared the seat (64A) was available on both, however when I went to select the seat under managing my reservation it was shown as unavailable, along with any other desirable seat (aka not aisle on the upper deck.)

(Note the flight is 2 months out, I’m looking to pay to secure this seat ahead of time.)

Is this something I need to call to assign?