Why bother with sorting EC 261/2004, when you appear to be US-based and US law requires a refund for a cancelled flight? File a complaint with DOT and then pursue the chargeback avenue below (both at the same time and both properly documented).
Presuming that you made your reservation and ticketing arrangements through SK and that you have made a request for a refund and it has not been initiated within 7 days, simply initiate a chargeback on the 8th day with your credit card issuer (bank). Supply or be prepared to supply a copy of the e-ticket receipt, the cancellation notice, your request for a refund and the denial or simply note that you have not heard back,
Most US card issuers will issue a temporary credit for a properly documented chargeback and it will become permanent in short order. The DOT complaint simply assures that DOT is aware of SK not abiding by its 2011 rules.