Mercantile Adjustment Bureau

I've been recieving calls from this CA on my cell and at work. The # is 866-839-7277. I called back and after asking for a DV from the woman who answered the call she immediately transferred me over to a very rude gentleman. During the conversation he became increasingly agitate when all I was asking was who the original creditor was. He kept telling me to be quiet and shushing me whenever I asked him questions. Finally he told me it was from Credit One Bank credit card that I took out in March of 08. I do own]e the money. The card had a limit of $200 of which about $150 was put on my Credit One for annual fee and application fee because I had very bad credit at the time. The rude gentleman told me my balance was now over $600 dollars and he wanted the full balance by the end of Feb. I repeatedly asked him for him to send me a debt validation which he refused saying that he was not obligated to do so. Is that legal? Also I asked for their address again and agian, and he told me that I have no need for their address. Now, I know I can get it from their website but is that legal either? He probably suspected that I was going to send him DV and cease and desist letters. I'm not sure but aren't they required to send me a debt validation when requested? Like I said I do owe the money but I want to make sure that if I pay them that my account would be paid in full and that my money isn't just going no where.