Beware of a software based "Infinity bug" which can installed on your phone just by answering and the caller usually doesn't say a word....only thing you might hear is a soft whistle. Once installed the infinity bug allows the perps to monitor your incoming & out going phones calls, but worse yet turns your phone into a "hidden" always on micro phone allowing the perp to listen in on your household or office conversations even when the phone is still cradled or on the hook and not being used!
With noting so many individuals having different stories in answering these call...most likely your phone was targeted and U are constantly being monitored.....Solution, at home buy a new phone hand set immediately; at the office inform your IT security to conduct a sweep and/or reprogram the office computer phone based system!!!
Skeptical...just Google Infinity Bug [both physical & software based] research, learn to protect yourselves.