I had this number phone me, only to hang up as soon as I picked up.
I called the number back and it went to a message saying 'call back consultants are currently attending other calls, please hold'
No idea what that's about.

full blown nuisance caller, doesn't talk but it's so you call back when you wonder who called you, some organization, I didn't listen to the ad. I blocked them, but they're calling every day anyway !

The caller is HETC - Online studying

called me twice today, I answered the second time, I kept on saying hello no one said anything on their end then they hung up... are they doing voice mapping.

Caller does not speak, stays on phone for roughly 20 seconds then hangs up. Nuisance caller.