Having recently moved house, I have become very aware of which companies have modern back end systems.
The most top-notch ones let me log on to their website, fill in a form, and all the address changes are made.
A few required me to ring up and speak to a human being, which was a little annoying, but not the end of the world.
Only one company insisted that I write them a letter. Co-Op Business Banking. Despite having a moderately competent website, they couldn't process a change of address online. Their phone staff were equally insistent that I buy a stamp, find a post box, and make one of their minimum-wage staff copy-type my details in manually.
Forget that noise. This is what I sent them.
Oh, and I copy-and-pasted a scan of my signature. Because that proves it's me. Right?
They didn't write back, but they did change my address. Which was nice.