I rang Powergen today. I got a message "Please leave your name, address and telephone number". So I said
"My name is blah, my addres is blah blah blah, my phone num"-
"Thankyou for your message"
I rang back a second time with my phone number. I didn't bother ringing a third time with the message, they can ring me.
It's like the sticky note labelled "Complaint Form" with a small box in the middle and the message "please write your complaint legibly in the box".