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.
Did not identify whom they were calling. Caller wanted a prompt return call. Are they serious? Who, in their right mind would return this call? These calls at ridiculous times are harassment. Send a letter if it is that important.