You should only be charged for the difference unless you are in another account. Or did you maybe also add a state or some other service?
Contact Customer Service
5am-9pm Pacific Time
7 days a week
What is the Turbo Tax phone number
OR.....did you buy the Desktop Deluxe program but end up in the Online version by mistake? I see people all the time that have bought the CD/Download Desktop Software but then somehow ending up using the Online version and didn't know it. If that happened to you, you can move your Online file to the Desktop program and continue without paying for Online or needing to reenter your info.