Update: Lufthansa still didn't respond so I filed a complaint with the superintendencia. Soon after Lufthansa denied my claim because "your request does not meet these criteria" for refunds. I filed an arbitration request with the alternative disputes regulator in Germany, which a few weeks later informed me that Lufthansa had declined to participate in arbitration.

Oddly enough a few weeks later I got an email saying my request for refund had been approved, and a few days later the money hit my account. (My guess is they finally got contacted by the superintendencia.)

So, keep pushing and eventually you'll get your refund...