Every French internet provider seems to want a French mobile number, I’m afraid. I don’t think there’s a way around it apart from getting a pay-as-you-go SIM next time you’re in France. With luck, you have a dual SIM phone so you’ll be able to have your UK and French numbers active at the same time.
As an alternative, you could consider Starlink. As it’s an American company I suspect that they won’t need a French mobile number. There are several happy users of Starlink here on Survive France. With luck, one of them will pop up and give details soon.
You could get a sim card router and french sim card like LeClerc or the post office sans contract sim. That is what I do as mainly UK based. Better than giving Elon Musk your money.
I’m trying to set up the wifi and mobile phone from the UK, so ideally I need a French mobile phone number that I can activate from the UK - is this possible?
Alternatively, can I just enter a made up french mobile number on the Wifi application form on the grounds that they will email me any important info? I’ve seen on other threads on here that people have made up numbers for deliveries but can’t find any specific info on wifi set up.
One problem you might have with a made up number is if they (Internet provider?) need to send a verification code. But give it a go and let us know how you get on, might be useful info for others in your situation.