I've been a Capital One customer for 10+ years. I have three credit cards with them and an auto loan financed through them. My credit score is 750+.
In the past five years I've had to call them to use money that is legally mine about 10-15 times, including once when they believed a transaction by LADWP (Los Angeles Department of Water and Power, a Utility Provider), who had charged me 12+ times, was fraudulently charging my card. They required a copy of the utility bill, my social security card, and a photo of my driver's license. After providing all of those forms of ID, they required me to get on a 3 way phone call with LADWP to have me provide my information, while they listened in, and LADWP then verified that I was the account holder and the bill was valid.
When they assumed the transaction was fraudulent on that one card, they completely froze all three of my credit cards, which was reflected in their web UI and mobile app. My debit card was not frozen. I assumed it was phishing at first, but after jumping through their hoops, my cards were unfrozen with no alerts or communication from their fraud department that the "investigation" led to nothing. I had to go check my account manually to verify my accounts were finally unfrozen. While this sounds absurd, I tried to use all three cards while they were locked, and sure enough, they were frozen.
The other class of issues I've had with them is in using my debit card - any time I try to use it, which admittedly is 3-4 times per year for an ATM, they deny the cash withdrawal. I then have to call them, spend 15-20 minutes on the phone providing my information, and then wait a bit before I can use my card to withdraw cash.
I would have switched banks the second I went through that ordeal with the utility bill, but one of the credit cards I hold with them is the longest credit line that I own. I believe closing it would negatively affect my credit, but I'd like to hear whether or not this is normal with Capital One.
The most frustrating part was the fraud dept told me they froze my account _because_ I changed my email. Nothing to do with strange charges on the account.