Save your efforts. Neither the callcentre nor the airport will help you there. Is just waste of time.

A lot of seats will remain blocked until last minute. There are multiple reasons.

Some rows in the Y-front cabin (usually 32 to 35 and some on the upperdeck) are blocked for their Top-Tier FF. Further seats are blocked for tour-groups (tickets are not issued and the TA has no confirmed bookings).

Travelagents have usually better access and can reserve seats without tickets being issued (as mentionend above). It is advisable to book via TA if seats assignment is really a concern.

Sometimes is worth it, to check from time to time as SQ may release further seats weeks ahead of departure. 72h prior to departure the seat reservation will be updated and most "dummy" blockings will be cleared except the seats blocked for Top Tier FF. Thats the best time to fetch a better seat. OLCI opens 48 hours before departure, early birds might be lucky here. The blocked seat for TopTier FF will only be released over the CI counter by the supervisor.