[Resolved]  American Express Card — Blocking of card

I had been a very loyal and trusted user of the American Express Gold Card for a few years. One day, suddenly, I was asked to pay all outstanding immediately, which I did without asking why. Afterwards, I was told that the same card was blocked and the call centers were not able to reason out why. One agent told me I had an impeccable record, and the other told me there was a problem. I was asked to contact their main office in Chennai, which I did. Even there, the same issue came up. One person told me he could not understand why the card was blocked, and one told me it was a decision taken by some superiors. Several requests to give me a proper reason were not addressed.
Eventually, one day, when my company was applying for a Corporate card, mine was rejected stating that I was a defaulter. I was shocked. This is absolutely false, and no one is accepting there is a mistake at their end.
I would like to take this to some competent authorities as this is nothing but a defamation against me.