Debt collectors are required by law to identify themselves clearly and not leave mysterious messages. The people who call from this and many other numbers leave only vague messages about getting in touch with them to resolve an unspecified matter, and they do not identify the person they are trying to reach. Nor do they identify the company they work for. (Wasn't that hard to find a company name, though: CKS Financial, a company known for acting this way)
As such, these people are shady at best and criminals at worst.
I have people calling me, for a person with the same name, who used to live in my town, now they google the guy's name and my info comes up, and once you square it with one of these scum bags, they sell it to another, and it just goes on and on. I not only get phone calls for this guy, I also receive his bills in the mail, to include his child support invoices, collection agencies, and even correspondence from the IRS. However, its the phone calls that bother me the most, they call at all hours of the day and night.
I have found the answer to all these annoying calls, it's called the Call Blocker, and it works great. I was looking for the solution to these phone calls, for years, and this is the best solution I have found yet. I bought mine on ebay, and it works like a champ.
Here is a link with the description for the Call Blocker.
http://hqtelecom.com/phone-call-blocker-manual-803/