First, let's talk about Ben's reactions. What are they? Hohoho. Ugh. Yes. No. That's all he'll respond to, even if you tell him everything. But what does it mean?
"Yes" means he is accepting something, he is agreeing to something.
"Hohoho" means that Ben is happy about something, or that something is funny to him.
"Ugh" is Ben's displeasure.
"No" is Ben's denial.
But as we have witnessed, Ben could say No (Ben's Denial) more times than he could say Yes (Ben's acceptance), and this is where my theory begins.
Ben has lost his sanity, and we are just a part of his imagination. Ben, by being in that damn green room, on that brown couch with that phone all the time, his sanity has come to an end. Why does Ben have a phone? Ben works in a call center, but he works at home, in that room, but his job was too long and never ended until he lost his sanity. His boss saw this and fired him, but that only made Ben imagine that someone else was calling him: us.
Ben's mind cannot accept reality, making Ben's answers demonstrate his denial, his denial that he no longer works there, that he must go touch grass. Ben has lost his sanity, and he proves it through phone calls.