This is a common scam.  Debt collectors call and try to scare you into paying them something because of a "bad check" charge which is supposed to be pending or  "check fraud" which you are supposedly going to be arrested for.  Sometimes they will pretend to be part of some vague law-enforcement like entity.  Ignore them.  Only public prosecutors and police can bring criminal charges, not some damn phony bill collector.  You can easily check these things out by going to the bank or checking with your local law enforcement people who deal in phone scams.

Invest in a call blocker.

Fraudulent or Zombie Debt Collectors—Things to Know

If you have received a call stating:

1. You have defrauded a financial institution
2. You owe an unpaid payday loan
3. You have a warrant due to an unpaid loan
5. You will receive a court summons
6.  Authorities are coming to arrest you
7.  Anything similar to above,
 a.   Do not give them any information or verify any information for them
 b.   Tell them you know they are a scam operating illegally and that you are   filing a complaint with the  appropriate authorities
* File a complaint with the FBI on their Internet Crime webpage     http://www.ic3.gov/default.aspx
* File a complaint with the Attorney General for the state you live in
The more information and complaints there are, the better the chance of getting these criminals to stop (or at least reduce the frequency).    [abstracted from another site]

They continue to bother  you, tell them you are going to the police to make a complaint of extortion.

These people use many different phone numbers.  So you are going to have to block a lot of calls, until these people get tired of calling you.