Then you should have sent them a. a certified, return receipt "not me" letter, b. reported them to the proper agencies, and c. sued them for FDCPA and TCPA violations.
Read up on your rights here and also make a complaint at this government site: http://www.consumerfinance.gov/
Also file a complaint with your State Attorney General's office.
List of State AG’s offices: http://800notes.com/faq/attorney-general