Email or fax isn't proof.. they need to mail you that via snail mail! And I copied this information from another post so folks are aware of this as its good information:

Extortion Scam Related to Delinquent Payday Loans

Washington, D.C.
December 07, 2010  FBI National Press Office
(202) 324-3691

? filed under: Press Release

The Internet Crime Complaint Center has received many complaints from victims of payday loan telephone collection scams. Callers claim the victim is delinquent in a payday loan and must repay the loan to avoid legal consequences. The callers purport to be representatives of the FBI, Federal Legislative Department, various law firms, or other legitimate-sounding agencies. They claim to be collecting debts for companies such as United Cash Advance, U.S. Cash Advance, U.S. Cash Net, and other Internet check-cashing services.

According to complaints received from the public, the callers have accurate data about victims, including Social Security numbers, dates of birth, addresses, employer information, bank account numbers, and the names and telephone numbers of relatives and friends. How the fraudsters obtained the personal information varies, but in some cases victims have reported they completed online applications for other loans or credit cards before the calls started.

The fraudsters relentlessly call the victim?s home, cell phone, and place of employment. They refuse to provide any details about the alleged payday loans and become abusive when questioned. The callers have threatened victims with legal actions, arrests, and, in some cases, physical violence if they do not pay. In many cases, the callers harass victims? relatives, friends, and employers.
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Please do file reports with the FBI, your state attorney general,FTC & FCC..

http://www.ic3.gov/default.aspx
http://www.fbi.gov/
https://esupport.fcc.gov/ccmsforms/form1088.action
https://complaints.donotcall.gov/complaint/complaintcheck.aspx?panel=2

Also read up on the laws and your rights:

http://www.ftc.gov/os/statutes/fdcpajump.shtm
http://www.consumerfinance.gov/askcfpb/search ...
http://www.consumer.ftc.gov/articles/pdf-0096-fair-credit-reporting-act.pdf

they are claiming to be from a company to collect debt from payday loans. When asked what the name of the company was that gave me run around saying many companies. I asked them to email or fax me a paper showing i owe the money. They will not produce anything. I dont owe any money to payday loan. in last couple years i have taken out 2 payday loans and paid them in full.