Capitol One Sudden closing of my account for no good reason Richmond, Virginia

I received notification  Capitol One stating that my credit card account was closed. The reasons given were as follows. We have observed activity on your account that is not consistent with our expectations of useage for personal, family or household purposes.
   My account has been in good standing, with a 30% balance, no late payments, always overpayments and I have excellent credit. I called the company and they would not give me any more information other than what the letter stated. I pushed for an explanation, but the gentleman said they have the right to close an account if the wish and basically said I should accept the decision
    I just think this is very strange because I have been a customer for a long time, paid all my bills on time and there is nothing unusual on any of my past statements. I tried to get information from the representative, but he was being very guarded. Now I am not sure if someone tried to use my credit card for something unusual or what is the real story.
    I just want to know the real story as to what they percieve as a valid reason to close my account. I also would like to be able to refute their reasons, as I feel I have kept my end of the agreement all through the years. I am also afraid this closing will have a negative effect on my excellent credit rating.