When the bill pdf opens either click on the printer symbol or press the Control and P keys together.
Otherwise you need to call up and speak to Billing and ask them to set up paperless billing, 150 from a Virgin landline, or 0345 454 1111,butbest to call between 8am and 10am to avoid call queues, or late afternoon around tea time
If you don't want to be tied up on the phone you could try the text messaging service. Just send a text with a description of billing to 07533 051809. Your message will go into a queue and a representative will respond to you as soon as possible. It may take a few days.
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali