Booking policy not honoured - one booking made for 2 passengers, but not seated together

My husband and I have been flying on Singapore Airlines for the last 10 years and are loyal Krisflyer members. We have made one booking for the two of us on flight SQ479 departing on 6 October 2022 (CT-Singapore). The system automatically pre selected seats 55B and 58A and which are not seated together. We have requested both via the Call Centre as well as the Customer Services e-mail address that their policy be honoured and 2 seats together be pre-assigned before the online check in opens 48 hours before departure. We have received feedback that there are no seats available. This is not acceptable and clearly a strategy to force passengers to pay for selected seats when making a booking. We have at no stage been informed that automated seat assignment could result in one booking for 2 passengers be split. We have been looking forward to our flight for two years now. We had to cancel our flight twice due to Covid, and are now understandably very disappointed to have to sit three rows apart for the duration of the flight from CT to Singapore.