your best option would be to try and gain the use of another phone to call the Team: 0345 6000 789 (standard rate call).
However you could try Contact Us > Mobile > Mobile billing and payments > Chat online.
The advisors are often busy though so you may not get connected straight away. (I recommend using a PC or laptop and keeping the page open, just refresh it every few minutes until chat becomes available).
If you want to say thanks > click 'Kudos'. Answered your question? > click 'Mark as Helpful Answer' also.