Problem

[Matt17]

No connection for 2 days now need my phone to work 

[Bambino]

@Matt17 See these guides:

How can I sort out my network issues? - o2uk

Why do I have poor coverage indoors? (o2.co.uk)

Wifi and 4G Calling explained | O2

[madasaf1sh]

@Matt17 

Have you tried your sim in a different phone? And see if you get the same problem? 

It might be you need a new sim card, best and quickest way is to pop to an o2 store with photo ID and get them to do a sim swap.. 

If you cant get to a store then you will need to call o2 and wait for one to be delivered to you (it may be after christmas as takes 5 to 7 working days to arrive). 

O2 can be contacted on 0344 809 0202 from another phone 

Also look at these guides Guide: How can I sort out my network issues?  Guide: Is the network down for me or everyone?