These guys are [***].  They give no good or verifiable reason for wanting to collect money.  I find that calling these types of companies back many many times a day for a few weeks and annoying the [***] out of them will eventually get them to stop calling you.  Also don't forget to ask for a supervisor so you can piss them off every time.  After a day or two they will know who you are when they pick up the phone and they will dread talking to you.  How ya like them apples.