The BCR collection agency is claiming that I owe money to AT&T Wireless, but I don't.?

I have confirmed with AT&T that my account is in perfect standing and that I don't owe them anything. BCR will not provide me with any details about the charges (the account number, telephone number ociated with the charges, etc.) but they tell me that if I don't pay them within the next week, my credit rating will suffer. It seems very fishy to me, but I don't want to pay them a cent until I know what the debt is for. It seems like a very straightforward issue, but having never dealt with a collection agency before, I don't know what information I am entitled to. What should I do?