Hey,
As you have not listed what you have done to help rectify the issue,I'm going out on a limb to say have you thought that the sim card maybe faulty or maybe your phone is.
Have you tried your sim in another phone and visa versa to try and rule each out of the equation ?
If removing the sim to clean it does not work then perhaps......
You could carry out a sim swap to rule that out......
http://swapmysim.o2.co.uk/
If you do this it can take from 2 hours to 24 hours to fully re activate and by turning your phone off and on helps resets all your services.
Blank Sims can be picked up free from an 02 shop.
If you have tried all of this then my apologies..... Just trying to help.
