How may I direct your call?

I was at work on Monday and the phone rang. I answered as I usually do, with a greeting, the name of the company and my first name. The rest of the conversation went like so:

"Hello, may I speak to Luis Garcia?"
"I'm sorry, but there is no one here by that name. You must have the wrong number."
"Oh, I'm sorry. May I have the right number, please?"
Pause.
"I don't know the person you're trying to reach."
"Oh. Oh, okay. Thank you."

Later, another caller asked for an institution other than ours.
Me: "I'm sorry, you have the wrong number."
Caller: "Would you transfer me, please?"

I'm a doctor, not a telephone directory!