Hi there, I would like to ask if Telecom charged me correct or not?

I was on Big Time and I changed to another internet provider.My billing cycle is the 16/08/2010 to 15/09/2010

On  19/08/2010 my connection to the new provider completed and I called Telecom to get my last bill (that's mean I only on the new cycle for 3days only).But Telecom charged me for the full month from 16/08/2010 to 15/09/2010 is that correct or am I overcharged?

Thanks