Number called my cell.  Let to go to VM.  Called back several minutes later and got recording saying I've reached customer service (no company mentioned; just "customer service").  Offered two options: talk to agent or register your number on do not call list.  Tried agent option and was told that all are busy and to send email with any questions to a Gmail address.  Tried do not call option and was read back the number I was calling from.  No I was not dumb enough to use my cell to call them; instead I used my work phone which sends main switchboard number and not my direct line.  In short, block this number.