@PSX_Defector said:
You can also block it at the SIP level with your provider. Do that along with international dialing, save yourself some headache.
If the SIP provider offers this, definitely. Using a route to do it stops your extensions (if compromised) from using them. Blocking them at the SIP carrier stops your PBX if compromised from calling them.
Neither stops you if the SIP provider is the one making the calls (looking at you, Megapath.)