If you visit ANY credit forum you will find that Capital One rarely raises credit lines on their starter or rebuilder cards. Also, from these forums you will see that people have been having a lot of luck with the Capital One Executive Office.
From another forum: Can someone PM me the cap1 exec office email? - myFICO® Forums
Go to the 6th response and click his link. You will find the CEO's email address (the link actually Google's it for you). Email them your GENERAL (ie no account numbers/no SSN etc) issues with the account. Be professional and courteous. Obviously, the CEO himself will not review the email, but he has a team of top level reps that will review your request and they will contact you by telephone (so include a daytime telephone number that they can reach you at). Many have reported recent success at getting a PC, APR reduction and CLI's.
And I have to say this: Capital One does not suck. They have weird, bizarre business practices on their starter/rebuilder cards for sure in that one would think that they would want to build a relationship with increased limits and rewards. But do they really suck? Who else will hand out credit cards to scandalous people that destroyed their previous credit (reputation)? Well, First Premier, Applied Bank, Continental Finance and Credit One that's who. And if you read those banks' terms and conditions, the horror stories about them etc etc you realize quickly that Capital One does not suck. Are they the best? No. Are they the worst? Hardly. Understand (again by reading the forums) that Capital One is mostly good for re-establishing yourself or starting out and they do it honestly and relatively affordably. But once you've made it, thank them for their consideration and then move on to the banks that actually want to give you higher limits and better rewards. But I do dislike the constant slamming of Capital One on these boards...Okay, getting off of my soap box.
Please let us know how it goes with the Executive Office.