Can’t access my web hosting anymore. Can I retrieve my domain?

Hi,
I lost any contact with my web hosting company.
I wanted to re-create my site by an other provider, but the wp install refuses my installation, as “An installation already exists at http://florence-gantois-hypnose.fr as per our records. To re-install the application please uninstall the existing installation!”
What can I do, since my previous hosting company hasn’t even been replying to my messages for 3 months?
Is my domain florence-gantois-hypnose.fr definitely lost?
Regards, Marc