They're scammers - NEVER pay anything unless they send you via MAIL a debt validation letter proving that you owe the debt to them.  They have also violated the FDCPA by threatening jail.  Report them to the FTC, the FBI and your state's Attorney General.  

If you receive any other calls from them - or other scammers - demand a debt validation letter giving original creditor, date of debt, amount owed, and if they are legally entitled to collect said debt in your state.  If you had written bad checks, you would have received a letter from your financial institution stating this, and giving you a chance to make good on them.  Also tell them you're recording all calls from them to give to the FBI and  your Attorney General's office.  They tend to back off some if they think you're recording them.  

Again, NEVER pay money unless you are sure the debt is yours, you receive the mandated debt validation letter and the company calling is legally licensed to collect debt in your state.  Make a note of all calls and try to get company names and addresses so you can report them.