I need to return boosters and avoid monthly charge (any ideas on address?)
You need to cancel the boosters.
You could try the text messaging service.
Just send a text with a description of cancel boosters 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.
You can also call 150 from your Virgin landline, or 0345 454 1111, but best to call at 8am to avoid call queues.