Nokia IMEI fix

My sister reported her contract phone when she lost it and I think the IMEI number was blocked by the network cause we recovered it and the network indicator is crossed out. I wanna know if there is any way I can fix the phone for myself. I know there is a way because the guys that fix phones do this but I wanna know how I can do it myself at home...

If you have purchased the phone, just go to their service center.

Try contacting the network about it.

Get a new phone..... or contact that network you phoned to disable that mobile phone to unblock it. please carry your phone box or any material that prove that the phone is yours maybe they can help.