Thank you for posting and welcome to the BT Community. I'm sorry if you're having problems viewing your bill online.
What happens when you try to view your Bill, do you get any error messages?
I have been using the website as I do not have the app. I have previously been able to view my bills, it's just the last one that was issued end of June. I couldn't view it but thought the system may be down or something so tried a week or so later and then forgot about it, unitil now!!