Go to your 'calling history' file. If you show the call as 'outgoing', it is YOU calling the default callback number to access / retrieve your voicemail messages. If you show the call as 'incoming', it is a number that is being spoofed by a hacker or robocaller computer. Don't sweat the 'outgoing' events and block the 'incoming' ones.
When I call my Consumer Cellular Voice Mail by holding down the "1", this number appears on my phone as an outgoing call. I just discovered that today. Scammers can evidently make any number they want appear as their Caller I.D. It seems our service providers could block any calls that have a caller i.d. that does not match the caller's real phone number. Surely.
This will settle it. 832-494-9000 is the ATT voice mail system. If you have a cell phone on ATT or a prepaid carrier that uses ATT, you call this # then your own # to retrieve your voice mails.
They are calling from this # to tell you that someone left a voice mail message.