This number 844-767-8544, calling themselves the Lincoln Group, called my ex-mother in law about some Wells Fargo account from 5 years ago they claimed I owe $600 on. They said they'd been sending correspondence to an address in Los Angeles I haven't lived at since 2009. Wells Fargo doesn't have this case info but they said if real, it would've been sold since then. The guy on the phone refused to send me anything in the mail over before I talk about a payment plan. (They had the last four digits of my SSN), saying they've complied on their part. They've sent me an email with a payment plan I need to agree to by 3/17. They said they had a "temporary hearing" scheduled for April 10. I have no recollection of this debt or overbalance, and cannot find it on my credit report. What can I do?