The first thing you should do is stop paying them.   Cancel your existing bank accounts and get new ones and notify the bank of a possible fraud.  Debt us a civil matter.  Being in ordinary civil debt is not a crime and you cannot be arrested for it.  If these people never sent you a debt validation letter, then you should not have paid them anything or agreed to.

Just because a voice on the telephone claims you owe a debt does not mean you 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 block their calls and ignore them.

If they are bothering you,

Report them:

http://www.consumer.ftc.gov/articles/0149-debt-collection  (Threatening criminal prosecution to collect a civil debt is a clear violation of the Federal Fair Debt Collection Act)

Also contact your local attorney general

If they continue to bother you, and you know you do not owe any money,  tell them that you know this is  a debt scam and that you are making a complaint to the police for extortion.  You might have to yell at the scammer and talk over him or her.  Once you get a copy of the police report and they call you again , just read out the  file number and the name of the PD or Sheriff’s office involved.   Tell them you’ll be glad to send a copy to them