If your goal is to have them stop calling, then I'd send a cease and desist letter. If you send it to them in writing, they must stop calling. Now they won't like that and may step up collection acticity.
The best option, IMO, is to send a DV letter. By law, they must stop all collection activity until they validate the debt.
Never, ever talk to a CA on the phone. They easily fluster people and anything you are saying is likely being recorded, which can be used against you later.
I can't comment on the BK, but maybe others can chime in. There may be a remedy there.