Caller ID was "CUST SERV." Did not answer because I do not recognize the area code. Left no message and subsequently blocked. That DO NOT CALL list is a joke.
You do not understand what the Do Not Call registry is or how it works. (But for a start, the call you describe did not violate DNC rules. It's not prohibited to call someone, get their voicemail or answering machine and not leave a message – if it were, most of us would be guilty. )