Actually, if you google that number, it belongs to a debt collector, not a telemarketer.
LTD Financial Services, LP
7322 Southwest Freeway
Suite 1600
Houston, TX 77074
http://www.ltdfin.com/index.htm
Caller ID: 866-998-2500
Caller: LTD Financial Services
Call Type: Debt Collector
Apparently this company had to pay the FTC a $1.3m fine back in 2007 for breaking various laws regarding harassment, etc.
http://aboutbrokerfraud.typepad.com/about_bro ... ve-debt-co.html
Here are the rules that collection agencies must follow, and how you can contact the FTC if you feel you're being harassed:
http://www.credit.com/credit_information/debt_help/Top-10-Debt-Collection-Rights.jsp
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Since they're debt collectors, you have to write them to stop calling.