I just went through the whole process myself to be sure of the result. So when it says the payment is due today it means the payment required to add funds to your account (not your monthly payment). Unfortunately it doesn't seem to account for disco...
I do have auto payment set up. Here's a screenshot of what I used to get there. really annoying design since to me it initially looks like an ad. Edit: you'll have to wait for the three 'ads' to cycle through to the ad funds option.
Try pressing the 'add voucher funds' button. For me it brings me to a page that allows me to add a voucher or use a credit card. By the way, I'm accessing the site from a phone.
