I have read numerous questions that do not address this specifically. In any case, I have received an invitation to interview but not interviewed yet, attempted reasonable contact and have waited a reasonable amount of time. See comments below where I refute claims of duplication.
BACKGROUND: I received a request from an internal recruiter for a phone interview and a time to do so. I responded the next day, suggesting that day was not good and opened up my availability for the next several days as well as offred up a suggested set time the day after the next. I received no response. As the suggested time approached without response, I called the recruiter and wanted to make sure I had not missed something so I could be available. He was unclear, but implied he hadn't heard from the person doing the interview, who is a technical supervisor not a hiring manager. I waited a week or so and received no response. I sent one more followup politely requesting more information either way.
THE QUESTIONS ARE: In the above scenario, 1.) do I only continue to try and contact the unresponsive recruiter and 2.) should I only use email or go to phone calls with them? 3.) How long should I wait to escalate and contact the supervisor? 4.) Should I contact the supervisor by email, phone or a message with the receptionist?
CLOSING NOTES: Yes, I already know to continue on in the meantime. Yes, I would still work for them after not receiving a reply. Yes, I know they hired a recruiter to schedule interviews as part of their duties so that the supervisor wouldn't have to deal with candidates. Also, the position is still listed and there is no closing date. The original invitation implied a desire to schedule the interview as soon as possible (but not urgently). I am not sure if the recent elections here in the U.S. have affected the process or not.