I’m wondering what my rights are in getting my money back for an upgrade charge I didn’t mean to purchase

Call me naive but as I was checking into my Norwegian Air flight online, I wanted to see how much an upgrade was and as I clicked on the premium seats the popup said the seat was 0 pounds extra so I thought it was free. When it came to the page to pay, I thought the price they gave me was the exact price I had paid for my economy seat, which was around 300 pounds, and that they were just restating that the price is the same and not the price is additional on top of what I already paid.

After I confirmed the payment I received an email showing the total price of the economy and the upgrade and realized I was wrong on how I read the price so I immediately called them for a refund and they said no.

I can’t afford to pay double the price for an upgrade. My flight is tomorrow. What can I do to get my money back? I’ve already asked my credit card to decline the payment but they said they can’t until the payment posts but my flight is tomorrow and I’m afraid once I’m on the flight in the premium seat then I definitely can’t get a refund.

Any ideas?