What does it mean if I called a phone and it rings then cuts off and when I call second after it doesn't ring and instead says "unable to call"? In o?

In other words, what happened to the recipients phone? Did they do something to it like what?

Updates
+1 y
It was a landline used to call a cell...
If that makes any difference I think not... indeed sometimes the landline says unable to call with other phones.
Updates
+1 y
I assure y'all I wasn't blocked by this person, lol.
What does it mean if I called a phone and it rings then cuts off and when I call second after it doesn't ring and instead says "unable to call"? In o?
Post Opinion