I'm sorry but not all agencies are out to get you and ruin your life by making you honor your debts.
If your credit card isn't charged off yet but in collections and you have an agency calling you then you need to contact the credit card agency and ask them where your card is place. Contact that agency, write your letter of validation if need be.. but you should also keep in mind that while waiting for them to reply you are collecting intrest late fee's and possibly an over the limit fee. Depending on the balance of the card you could be collecting fee's from 30-200 dollars a month if not more.
Most agencies who actualy follow the rules are apart of the BBB. Do a little research. You obviously have access to the internet so do a search on the company. Pull your credit report as well if you haven't gotten your free one or go to the CBR websites and purchase one.
If you are not satisified with the information you have found out about the company write them a cease and desist letter which they will forward to their client and place it with another agency.
I'm not saying the debt validation letter is a bad idea. It's not. But durring the thirt plus days you get one (allowing for 3-5 business days of mailing time from you and them from them) it is higly likely that you are going to be hit with a shot of late fee's along with a side of intrest with an over the limit fee to follow as a tastey dessert.
And I'm not talking about credit cards that have been charged off already. I am talking about precharge off. There is a HUGE difference.
If you are in entirely too much debt your best option then might be to go with a credit counseling service when they dispurse payments you make to them to each agency owed. But the most important part of this is to be sure, 100% sure you have an accepted proposal. Not all but most companies will work with you.