Originally Posted by demue

I'd still send an email to SQ Support putting "urgent / high importance" label on it and stating it is for upcoming flight.

​​​​​​Tell them you have been trying various ways for hours to get in touch with one of their customer service channels but to no avail and state your request (e.g. cancel flight etc.) Also provide contact details.

At least they cannot say later you never reached out prior to your flight. YMMV.