My last job was in CSR with a very small re-sale phone co. Once a month we were all expected to make collection calls to customers who were late with their payment. After several attempts one day to a particular number, a lady finally answered.
Me: May I speak to ___ (customer's name)?
Lady: He's not here.
Me: This is ___, with ___Phones, your phone company. I am calling to remind you that your phone bill was due on the 5th and is in danger of being disconnected. Can you tell me when you will be able to pay it?
Lady: .... How did you get this number? It's unlisted.
Me: *blink*... Ma'am? This is the phone company. We GAVE you this phone number!