A debt they claim I owe with speedy cash (pay day loan)

I received a message from Andrew Law Firm that I owed $400 from CashnetUSA/Speedy Cash/Cash Advance.  There is one problem with this and that is Speedy Cash has always been paid up and I have another loan out with them now.  They would not have given me another loan if I owed them money.  These people want me to send payment via vanilla debit or American Express Debit and they want me to submit pictures to them through their email along with the receipt.  I have never heard of a law firm doing business like this.  The last email I received has threatened me with jail time.  This is the most absurd thing I have ever heard of.