But how did it happen in the first place? .50 cents per minute and I would like for it to not happen again.
Call forward is setup by users though. Which phone are you using? There is an option in phone settings to check for that. If you actually would like to setup call forward, you can add the add-on for $5 in self-serve.
Regarding the history, you can look into the call log in self-serve to see when the forwarding started. From there, you could see if any device change, or phone firmware update happened during that time frame.