Do not answer unknown calls and do not call them back. Consider getting a call blocking device (or app for your cell phone)-they're available online and start around $45. http://800notes.com/nb/search?q=call+blockers
I'm not certain if this person is who he says he is or from the company that he said (and wouldn't want to denigrate actual people with those names), but the other posts about this phone number's caller are exactly what I experienced (incl name). This caller reached a colleague of mine and lied about talking to me previously, in order to trick the employee into thinking it was a legitimate call and 'getting through.' Clever but unethical and deserving of another post here.
Alan (with a thick accent) from Enosis just called the office I work for and asked for a staff member by name. She stated she did not know who he was and when I asked to take a message he asked for someone else by name then refused to leave a message. The CID only lists this phone # and Op.