If they have settled with you in writing, then they have to honour it.

The only people that could tell you what/why it is taking so long are Capital One. My suggestion would be to call them again, and wait this time. It's beyond frustrating when customers call up asking for advice, and then hang up whilst you're checking things for them with other departments (I do not work for Capital One, but I do work for another credit card company)

If you're that bothered about it, you'll hold. If you're worried about the cost of the call, ask for some compensation for the calls, believe it or not, credit card companies are able to refund money to your account for such things if you complain enough and have a genuine reason to complain.

Patience is a virtue, good luck.