Finally sorted - I went to the SQ centre at the ION Orchard. They weren't able to help directly (as they only deal with airline issues and not Krisflyer/PPS matters) but sent a message to the relevant team to encourage them to get in touch with me. A few hours later I got the email confirming PPS status and I already moved my all my upcoming J flights on the B777 to row 11

Persistence pays off, only 6 1/2 months after my original email to SQ!