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since you have cards from other banks, just focus on using those cards to improve credit, I'm sure once your credit is better, then capital one will bombard you with their pre-approval letters. My first real credit card was from capital one 11 years ago with their platinum via card with 300cl, I had few store cards but that was it. maybe like others mentioned with total credit you have might have something to do with your debt : income ratio or whatever.
Par for the course for Cap1. Ditch them and never look back. It was one of the best credit moves I ever made. $0.02