The OBiTALK web portal overwrites the local device settings, so setting it on the local interface is just going to get wiped out the next time the portal resets it.
Set it on OBiTALK. And, if it isn't being changed on the local interface, then perhaps you have disabled or otherwise changed OBiTALK provisioning.
As always: pick a configuration management method and stick to it. Don't try to configure it in both places.