I just called this number and got increased $500. I've only had my Capital One account for 4 months. Also, just this week i got the automated CLI increase of $250. My CL went from $500 to $1250 in 4 days. I'm so glad i found this thread. I also asked how often I should call in and ask for an increase and the service rep, John, indicated I should call every 6 months. I've bookmarked this thread for future use.
04/18/18: TU-677 EQ-747 EX-756