I am not a Nokia C5-03 user, but here is the rough guide about how to setup a new access point:
Go to Menu---> Settings ---> Connectivity----> Destination ---> Internet
To make things simple:
Delete the Diginet regardless of its priority
Then, go to Options at left corner of the phone,
Select " New access point"
when asked to automatically to check for available access point, click "no"
After that select the "Packet Data",
When asked for the Packet data access point name, just type in "3gdgnet"
After that, you should be able to surf using that access point.
Happy Surfing.
O, ok thanks. Can surf already. Make sure it won't "DC" so easily anymore.