I've just been having this issue, but in reverse: I've been burning a big stack of Airbucks but have Velocity Gold. My findings:

1) FQTV vs FQTS as nomenclature are useful: but I found that calling it the "FQTS Non Accrual field" got the best results.

2) Quote your number with the airline code. My Velocity number got stuck in as VS1234567890 rather than DJ1234567890, which meant no seat selection for me.

3) The evening shift seem to be more comfortable dealing with this stuff, whether that's because they're more experienced or whether they're bored and keener to chat and poke around with the system.

4) Eventually, you'll run into someone who refuses to believe this is possible. Time for call centre bingo: thank them, hang up and ring back.