Yes a sad story that and I must admit something similar happened to me when my mother passed away and I attempted to transfer the Scottish Power account to my name - so it’s not confined to French companies.
Anyway too early to say how my issue with Bouygues will resolve. A call last week to them indicated there was nothing more for me to do but then today I get an email saying I have to return equipment that was returned automatically as I didn’t pick it up. It’s all so predicable from large companies. I used to work for a company taken over by BT and all the staff were not taking broadband from BT despite the staff rates but rather from Plusnet. Word got round to senior management so they bought the company but have not tried to interfere in how it is run because they know they will screw it up.