The phone worked OK for the meeting, though I missed the large screen and multi-person view and I also used up all my free data allowance. But when the internet was still not back after the meeting ended, I knew I had to try to contact the ISP's support people.
Now finding out how to report a problem with your internet when you have no internet is not actually easy because all the help is provided online! Thankfully the 4G signal was OK and after going round the help pages on the website several times and not finding a way to make the router connect successfully to the internet, I finally managed to find the help text chat.
First you have to negotiate the help bot, but after it had failed to understand two of my questions, it helpfully connected me to a real human being who was helpful. He/She ran various tests and said the fault was indeed on line and not anything wrong with our equipment. The fault has been traced to a nearby exchange, a fault report has been submitted and an engineer will be on to it within 24 hours.
At least I hope so. I'm typing this at just before 3 p.m. on a Sunday afternoon and I wasn't expecting anyone to get to it until tomorrow, though I just had to break off to answer the phone and it was an engineer who is investigating the problem. He says the line is OK but that it's a software problem in the box thing where all the connections are. (OK, he didn't use the phrase "box thing", but that's what I think they mean by "exchange" these days.