I couldn't get online at all on Monday, so I rang Pipex but their helpdesk closes at 9pm and I was 5 minutes too late. I rang my mate, who is also on Pipex, but she could get online and was OK. She checked the website and it said that there were no service outages.
I rang Pipex from work the following morning and the girl suggested that my firewall was blocking access. I knew it wasn't, because it worked perfectly before, and firewalls don't suddenly reconfigure themselves.
When I got home from work on Tuesday, I still couldn't get online, and rang them again. After being on hold for 17 minutes, at 10p per minute, I got through to a very pleasant chap who started on the standard script of reboot this, unplug that. I stopped him and said I'd already tried all of that, and that the problem was that the DNS was not able to resolve IP addresses. "Ah!" says he. It turns out that they changed the DNS at the weekend, and he gave me the new numbers, and bingo! it worked.
Surely it is not beyond the wit of man to realise that if the ISP was changing the DNS, that they could have e-mailed all of their customers to tell them of the change, rather than just cutting everyone off? Surely they could have put something on their website, so that people logging in from work, like I did, would know about the change and not have to spend ages on the phone trying to sort it out? Or perhaps they just wanted everyone to ring in and pay their 10p a minute to boost their coffers?