It's probably no consolation, James, but phone problems aren't confined to France. I've spent a good two hours today trying to get BT to send me two screws to secure my "master socket" properly. I think I lost them during a rewire 20 years ago. I could bore you for, well, two hours with tales of the unfathomable BT website and unfruitful conversations with call centre staff. But I won't. Suffice to say, I finally found the size of screws I needed and ordered them from Amazon. The alternative seemed to be to summon an engineer, who would install them for £108. I hope you find the answer to your problem more easily.