Samsung Galaxy S2 — Extra digit added to incoming phone number

I recently had to reset my samsung galaxy s2 on ICS to factory fresh as a downloaded app gave me a virus causing constant reboots. Now when I receive a text or call from one specific person the number shows as 07752.... whereas is should be 0752..... this has the result that when I reply to the text it never gets there and is lost. I have to open a new message and select the correct number from my phone book. I called vodafone who recommended resetting factory defaults once more but it's still happening. I've also tried deleting the contact entirely from both the phone and my google contacts via a PC. All other contacts work as normal. Any thoughts?

UPDATE:
The phone is now working fine with the contact. When I reinstalled to factory fresh I also restored the call logs from Kies. The call logs showed the 2 different numbers and was in fact the way i discovered the contact wasn't receiving my text in the first place. Anyway, I deleted the entire call logs and rebooted the phone and am now having a normal text conversation with him. I still don't know why the phone kept persisting in altering the incoming number but at least it's working now.