We applied via the online system and had to provide screenshots/photos of payslips. We've had to reconfirm every 3 months and they've not asked again but definitely call them and you could probably submit it online. It may be due to your youngest starting.
I had an email asking and called up to get a wetransfer link then attached the screenshots to that and they were happy with that
No i didnt get a letter. I’d ring the number to ask for an explanation. They’ve been helpful when I’ve had queries x