It looks like your phone still hasn't enabled root permission from the secret menu:
- On the GW620 dial "3845#*620#" to get in to the secret menu
- Tap "Module Test" then tap "Stability Test" then tap "Enable Root Permission"
Do this again, and then "adb remount", then "adb shell".
If it still doesn't work, try restarting both PC and phone, and then enter the secret menu again.