Did you get charged by Costco, and then when you tried to download/install, you got charged again but the second time was by TurboTax? I don't know why it only offered you a "Buy Now" link instead of a "Download" link and charged by TurboTax, but it sounds like you somehow ended up with a duplicate purchase. Costco won't normally remove a charge for a software download, but TurboTax will.
Phone TurboTax Support and tell them what happened and that you ended up with a duplicate purchase and ask them how they can resolve it. During filing season they are currently open every day 5 AM to 9 PM Pacific.
FAQ: What is the TurboTax phone number?
https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/turbotax-phone-number...
Also, if you haven't been able to download your purchase, ask them for help while you have them on the line.
