Thanks for sharing. It seems to me that Capital One representatives don’t have a clue about the products that they offer. What they told you about only the initial deposit being refundable is NOT true.
I had this card for about two years, and I made several extra deposits to raise my credit limit. When I closed my card, I received a full refund for the total of ALL deposits I made. I know this still applies today, as my wife just closed her Capital One secured card two weeks ago, and she received a full refund last week (and she also made extra deposits).
Now, if you are given an unsecured credit limit increase by Capital One (that is without you making a deposit), which are rare but do happen, then of course this amount is NOT refundable as it would be an unsecured increase.
I suspect these people are just reading from a computer. If you are unsure about this, I would call customer service. I’m sure you’ll get a different answer.