One week to respond to a letter delivered by US postal mail isn't really much time. Not that I support Flock or the concept of Flock-style public cameras, but I don't think you can judge them to be "not responding" that quickly.
Seems like their PR fire is self induced by sucking up to Money and whatever they qualify as investors?
Why not? Because it takes long to deliver, or because they can't be expected to read their mail?
Companies can move mountains yes, but a routine request to cancel a service probably isn't seen as requiring that. Especially since the service contract undoubtedly defines the terms upon which either side can cancel.