Data Point.
Not a cancellation, but a change of one flight on a 3 flight PNR.
Changed a J flight BKK-MEL on TG to 3 days earlier than the original booking.
On the phone to the San Salvador number at 11:00 pm Melbourne time. 7 am San Salvador time.
Took 20 minutes and all was confirmed and paid (USD $300 for 2 pax - CC info entered via keypad) with no stress or issues.
Update itinerary and documentation in my email within 5 minutes.
Selected seats on the SQ mobile app.
Checked on Amadeus and all bookings/seat selections updated.
No complaints from me. Very smooth.
Interestingly I was never asked for a PIN or to confirm DOB or any other ID. Just PNR and Last Name of both pax.