Which one of these can sue me?

The original acct was a GM card issued by HSBC. The account was charged off and subsequently sold. The credit report shows the trade line as sold with a zero bal. by GM. The acct. was apparently purchased by a JDB by the name of The Bureaus. Credit report now shows a collection with The Bureaus.

I was not able to settle for the outrageous amount The Bureaus offered so I stopped answering their calls. Now I receive a call and dunning letter from Sentry Credit. It says they have been assigned to collect for Bureaus Investment Group.

I wasn't aware that a JDB would farm out an acct they purchased to another CA for collection. My question is who can legally sue me on this? I would assume that the GM is out of the picture since it was sold. Can Sentry sue me if the debt was purchased by The Bureaus?
Thanks for any help!