It's now been 6 weeks since my flights ex ARN were cancelled by SQ and I applied for a refund (revenue tickets). I've still not heard anything further from SQ.
They've had enough time to refund a perfectly simple ticket so I have asked Amex for a chargeback which they have agreed to do (and a dispute credit has already appeared on my Amex account). SQ can contest if they wish to but I can't see anyway they will succeed.
It's sad that I've had to resort to this, SQ knows I'm entitled to the refund so all they've done is alienate me so I'll go elsewhere for my flights in the future.