Harassing Phone Calls on my cell and at work

Last summer in 2010 I was contacted by this man saying I owed on a loan and if I didn't pay it now that I would be going to jail for none payment and more money added for court and attorney cost.  So I made three or four payment arrangements throught my bank card, he said once the amount was paid in full that I would receive a receipt in the mail, I NEVER RECEIVED ANYTHING.  And now just as recently as this past week.  I was contacted by these number 863-438-1785, 772-252-9282 from Florida and another from California 530-287-4269.  But with me I was so freaked out and scared that I made a payment of three hundred dollars to them.  I know now that that was a BIG MISTAKE, but since then I have looked into trying to find out who these individuals are, but of course turned up nothing.  These are very stressful, they've even contacted my work. How do they get our information so easy?