What does Unwanted[31] mean?

As the tittle says, calling a specific number Im getting that are the response code.
What does it mean?

Can you posted the whole response, or section of the log?

Unwanted[31] must have a corresponding freeswitch cause which you need to find in the freeswitch call log. Set the log level to 9 and enable SIP debugging to get the actual reason the call is failing. The freeswitch hangup causes are explained here:
Freeswitch hangup causes

Fixed now, customer accidently added number to a call block. Showed unwanted on the phone itself and ASTPP.