Legal/arrest threats

I previously had 6 payday loans (all internet) upon finding this forum I closed my bank account and sent letters of revoke of ach to the companies. The only company who has responed is Khaki Funding (Loanshop) I paid $720 on a $300 loan and I live in South Carolina. They have called 27 times in the last 4 days. I got a phone call today from Robert Foster (1-866-669-3182 ex.3291) who would not state the name of the company he worked for, only that he was working on behalf of Khaki funding. He said no matter what our state laws are we were obligated to pay him $300 today, or he would contact our local authorities to have me picked up for fraudulent check writing and notify the check writes system and I would never be able to write a check again. Then said I was using my Social Security number fraudulently and could report me to the FBI. What should I do?