Lilly calls cameron to invite her to a party, leaving the message on cameron's voicemail. after two days, cameron still hasn't returned lilly's call. lilly might interpret this as what type of response?

The answer is an impervious response. An impervious response is one of the seven types of disconfirming messages. We can simply put this as "No response at all" because an impervious message fails to recognize the other person's communication attempt either via verbal or nonverbal way; failure to respond in all forms and channel.

It is called impervious response
 This type of response ignores the other person attempt to communicate. the person acts oblivious of whatever was said or communicated. It is the highest level of dis confirming where the persons completely ignores the other person message regardless of receiving it.

More context .

The ceremonial column.