Product with option not correct

Scenario:
We offer a product for $6.95 (10ml) with an option for a 30ml upgrade for $16.95 (+10.00). We created a product in an unpublished category and added characteristics (this became the 30ml upgrade option for +$10.00) to the original product.

Problem:
We had an instance that the customer was only charged the option price of $10.00 instead of the $16.95. We verified that the category was unpolished and setting was correct. This could be a huge issue especially if the customer is only charged a small fraction of the total price.

Thanks for your help.

Hi there,

I will need some precision. Your main product have to be in a published categories.
It's your option which have to be in an unpublished category. In this case, customer will not be able to order only the option.
Second thing is in the case customer delete the main product. You should try to enable the "Group options with product" (System>Configuration>Main>Cart) so the option is removed with the main product.

We had all that right so this a.m. my client emails me and said the staff read the invoice wrong and the way it printed out confused them. So bottom line things are ok. Thanks for your continued awesome work.