There does not seem to be a way to block annoying incoming call centre callers. All options on pre and post android system methods aren't available. I have tried many different options. This particular call centre I have told them how i feel about there annoying calls and now they ring more often late at night early in morning. I'm honestly thinking of going to the ACMA (Australian Communications & Media Authority).
I know they have me on their most wanted board because I played along and would leave the phone and work for 5 minutes and come back and play a bit more and leave it for 10 minutes and She really got upset. That when I told them how annoying their calls are how does it feel?. Now I've made it worse but I think they have no right to harass.