Unfortunately there is no quick fix for your particular situation (I know, I was there once too!). Spending a lot (but not near to your limit before paying down) and paying it off quickly may help (one way is paying all your bills with the card that you'd normally pay by check/debit). In particular, if you can demonstrate the ability to pay off more than your current credit limit for several months, in my experience that has often triggered limit increases.

For example, you'd charge $500 on the 1st of the month and on the same day schedule a payment for say the 5th. Then on the 8th of the month, spend another $500, and pay that off by the 12th. Repeat two more times and you've spent $2000 on the card that month and end up with no balance.

That's a perfect end-of-month for the credit card company: you've spent much more than they ever put at risk (since at any given time you were capped at $750); you generated higher transaction fees than most of your cohort with that same card/limit; and finally since you have no balance you are at zero risk of default.

If you legitimately need the kind of higher limit you're looking for, you should have no trouble spending like that (and if you don't spend like that, you don't need the higher limit), and after 3-6 months of doing just that, I bet Capital One will up your limit automatically.