No reply to my "Hello" then a womans voice on the recording saying "Goodbye"

I got a call from this number as well. When I answered it, there was no sound.  When I tried to call it back I got a recording saying that this number didn't exist.

we have had three calls from this number but we do not answer

2 calls from this number and call backs say that the number is not in service.

This is a call regarding a mobility plan with no obligation.  Do not believe that myself.  
It is very loud and hard to understand what they are saying.  I have had 6 calls in the last week from them and I keep saying no thank you and they call the next day.  
They ask for you to say yes to the offer and give it to a family or friend as there is no cost to you.