Hi,
This issue comes from the customization of your product page which was not done properly. The way it's done, the data of the product and its options in the hidden input fields of the product page are outside the main form of the product page.
The easiest solution will be to contact the developer who made that customization for you so that he can arrange the code to work properly all the time.
Otherwise, you can also remove that customization and use the default view of the product page and it will work too, but I guess that you want to keep your product page design...
Regarding the prices being displayed twice on the page, it also comes from the customization. As we don't know how it was done, we cannot help on that either.