Get them to start calling you on your "new" number which cost them a huge sum to call. Then put them "on hold" why you consult your finance department over the outstanding payments they keep calling you about.
It's good to vent out our frustrations and anger on others especially when they are asking for ideas.
It will be interesting to see what the French courts will come up with against this so called "Church". I am sorry but I can not take anything from them seriously. I am how ever impressed that they can get away with all this all over the world.
Writing and speech is one of the slowest forms of communication. Once we have enabled us to communicate more efficient, someone out there will be happy to point out that it will only make us "slower" or "dumber" as it is far easier to condemn then to embrace.