Did collector buy debt or are they working for AmEx?

by Irene
(Washington State)

How do I find out if my debt was purchased by the collection company or if they are really working for American Express?

I have been paying on the debt to one collection "lawyer" for about 18 months, a huge amount each month. I can still go into AmEx online and see my balance and it is going down and shows each months payment. However, where it says Minimum Due, it is far lower than what the collection company is asking me to pay.

Now I absolutely can't pay, and a few months back I called to re-negotiate the payment and told them what I saw on AmEx online and she asked me where I saw it, so I told her logged in and there it was. She said "Well, you aren't supposed to be able to see that". Makes me wonder.

Can I just start paying the minimum due to AmEx directly and tell the collection company I'm not paying anymore? What might happen?