No debt collector has anything to do with either garnishment of wages or levy on assets. Those kinds of things can only be done on the basis of a court order as part of a legal proceeding in your local court system. Ignore and block these calls.
Report them:
http://www.consumer.ftc.gov/articles/0149-debt-collection (Threatening civil proceedings with no intent to follow through, or threatening criminal process in order to collect a civil debt is a violation of the Federal Fair Debt Collection Practices Act.)