The annoying thing is the letter (yeah, she didn't even phone me) arrived this morning, and I (frustratingly) can't do anything about it 'till Monday!
Oldest trick in the book that, mate!They work Monday to Friday. They have letters that they know are going to annoy people, and post them so that you get them on Saturday.
What's your initial reaction when you got the letter? Ring them up and shout a bit? Demand an explanation?
You've now got the entire weekend to calm down before they have to deal with you. :)