Cannot use mobile data because it is so slow.
@SQ1 See if there's anything in these links that will help you:
How can I sort out my network issues? - o2uk
Why do I have poor coverage indoors? (o2.co.uk)
Tips to make the most of your mobile data - O2 Community
I DO NOT WORK FOR O2
Track usage, upgrade and get support with the My O2 app