When i connect my phone to wifi, how comes it still charges me for internet?

Hmm. Does your bill show large amounts of data, or only a small amount (either in terms of cost, something like 2p, or 10Kb)?

I used to have a problem with my Nokia N82 that when I used the GPS map facilities, despite telling it not to connect to the internet, it always did, and it always used GPRS to do it, causing me a charge of something like 2p each time.

This didn't stop until I reset the handset to factory settings.

It may be that a similar thing is happening with you, particularly if the charge is for small amounts...

What might be happening is the attempt to active a GPRS context on the SGSN is what is still resulting in a CDR being raised by the SGSN, but the handset then fails and uses WiFi.

It would depend on what exactly your contract says, but if you're not supposed to be able to access the Internet, then how can you be chared for using it?

The fact that Vodafone's network is not stopping you doing something you're not supposed to be allowed to do, is not your fault - it's their responsibility to prevent it, and you have no obligation to pay for it.

The flipside is that if the bill is showing large amounts of data (i.e. the whole browsing session is on GPRS/3G and not WiFi), if they fixed whatever is allowing you to still use the mobile internet, you'd only then realise that your internet access isn't working, whereas you'd previously been happily thinking it was working on WiFi.

I use my WiFi at home (though rarely for mobile internet - the screen is just too small), and you have to make sure that your access point is correctly set up on your phone (my guess is that if it isn't the handset may be failing over to GPRS, which is why you're being charged (even though you shouldn't be allowed)).

How to change the settings will be dependent on the menu options on the C3 (I can't be certain that my N82 has the same options as your C3, so I can't guide you), and the WEP encryption key &etc. on your router.