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It turns out US embassies in a foreign country will respond if you write an email to [email protected].
After filing a case there, I was able to obtain a separate email handle with which to discuss return of my passport and possible cancellation.
Edit: US embassies allow you to temporarily retrieve your passport and/or I-20 without cancelling the visa application. This will put processing of your application on hold until you return the passport/I-20. You will be provided instructions on how to proceed with this after emailing the consular office - in my experience, I ended up visiting the consular office, collecting my passport as well as notice of temporary suspension of processing, and a return address to mail my passport back through an official courier once I was done with my use.