Collection Harrassment

I took out a payday loan from Multiloan Source on line. Honestly I did not pay back all the money my account got out of hand and the bank closed the account. Someone is contacting me indicating that they are a processor and that Multiloan closed my file. I bought a prepaid visa card from walmart and thus far have given them 320.00 I believe that they say that I owe 920.00. I asked them to send me something showing how they acquired the debt and what the original amount was from Multiloan. All I know them as is USC with different phone numbers. They said that they sent me a Letter of Intent which I never received therefore asked them to send me another one and I offered to pay for the postage. They because downright hostile indicated that they would put my money back on my card (which they haven't) and will move forward with serving me on my job job job is thrown out there a lot. At anyrate I do not plan to make another payment until I receive something in writing doesn't that seem normal? I told them that the Multiloan could come back and say that I still owe them and they said oh no that won't do that I said how do you know. At anyrate the only thing that they will acknowledge in sending me is a paid in full letter. (That's not good enough for me). Any suggestions:rolleyes: