Nokia :: N97 Connection Error Message When Try To Make Call

My n97 was working perfect til i installed the latest updates, since then all i get when i try to make a call is "connection error" and a yellow triangle with an exclamation mark in it, I cant receive phone calls either it goes straight to voice mail...The phone was sent to a repair center where they fixed my charging problems, replaced the camera lens and never bothered with the "connection error". Ive sent several emails to Nokia but no response, the phone is almost 6 months old and is on Vodafone, Ive tied another sim card in it and still no joy...Plz help as £300 is not good value for a 6 month old phone,