@selamawit24, hi there, is your phone unlocked 🔓 or on o2 for giffgaff sims to work, it can take upto 24 hours to fully activate if still having problems contact an agent as they are the only ones that can deal with your account.
Since you're not able to use your phone service then please check your area coverage from here: http://status.o2.co.uk/ Just by entering the area post code.
If everything is Okay, then reboot your handset just by tuning it off and on. Hopefully, it will work.
If you're still facing same issue, try your SIM in other unlocked handset and vice versa. This will help us determine whether the fault is with the handset or the SIM. If the SIM works in another handset then it's a handset issue which you will need to address. If the SIM doesn't work in any handset that means the SIM is faulty and must be replaced by doing a sim swap.
It's more than 24 hours already, like I say I've payed £15, five days ago I still can't used my phone, it their anything you can do to active my sim? I really need a phone I can't stay any longer with out phone my number Is>**phone_number_removed**