Earlier quoted context omitted.
It's just as bad in Europe! Signed up to O2 Deutschland - had to send a fax or send a physical letter to cancel.
That's illegal in Europe. You have to be able to cancel via the same means as you signed up. So if you can signup online then you must be able to cancel online.
Unfortunately I don't think that's true. I'm looking at you, beer52.com! [1]
(And yes, they were doing this long before the UK left the EU, and are still at it today)