I was looking for Add Ons for Destiny 2. No bundle has been displayed. So I bought three AddOns seperatly. Just as I completed, a bundle has been displayed containing the three AddOns and extra Stuff for less than I paid. So I immidiatly claimed refund for the three packages and paid the bundle. Refund was denied, due to Policy. So I paid twice for content, that isn't properly displayed in first place while there is no search on google stadia ... ...
Maybe it's an idea in your case to contact the Stadia team in this case. Maybe an exception is possible for your situation? Otherwise there might be a reason why the refund has been denied and then the decision stands, but I guess it's worth a try in your situation especially if it wasn't pretty clear for you when buying the bundles.
Neither Stadia Team, nor Google want to be contacted. Your link offers three options besides the faq: Chat (closed), Facebook and Twitter. Also you can't call Google. All numbers lead to nothing. Each way to choose "talk to an employee" terminates the call after a few seconds. Worst service ever. Stadia has no search option, and google no way to attend to customer issues, besides the faq. The links to Twitter and FB aren't Support pages either. The message is clear. Spend money. Don't complain.