Just because someone on the phone calling you says you owe a debt does not mean you actually owe it.

If a voice on the telephone claims you owe a debt:

1.    Demand the person give you his or her name, company name, and address
2.     Demand a debt validation letter by US mail.  E-mail no good.
3.    Do not pay  the collection agent or anyone else a  dime until the debt is validated

Of course they won’t do this, no scammer ever will, so simply ignore them and block their calls.

If they are bothering you, 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.)  The same goes for endless telephone harassment

Also contact your local attorney general