You have to use the number on the back of the card. It doesn't give you a specific option. You are asked purpose of call. That is where you say "credit limit increase". Then it asks for income and if you want a specific amount and that is when you say "no". If it works, then you repeat the steps. It gave me increases in $300 increments. So I was able to make the request 10 times, then it stopped working.
