You used to be able to do this from your Transactions page but, as far as I can see, the PDF bills are no longer listed there for some reason:
What do you need them for? If it's for proof of address for some other purpose then they'll be no use anyway as they don't include a postal/residential address.
If you need to contact 48 support about this then see the links in my signature below.
Edit: my mistake - you need to choose the Download Payment History option on the Payment screen and then you can download a PDF of the bills for the selected time period. The PDF bills used to be presented in a different way so they must have changed it at some stage in the past.
