It's a well known scam.
Block the number and do not follow any links.
Forward the scam text to 7726 - It's free.
Other ways to report here including Action Fraud website
How to block a number:
O2 never text from a mobile number.
Please also remove the link to stop others clicking on it.
I got same text early hours just deleted and blocked it and went back to sleep
Without doubt the right decision
Track usage, upgrade and get support with the My O2 appDownload My O2