If you need a refund, your records do the arguing for you.
The confirmation email, the order number, a screenshot of the package, price and guarantee on the checkout page, the card charge, tracking and delivery dates, and the refund policy as it stood on your order date.
Keep your daily log too.
Put everything in one folder and note your refund deadline in your calendar. If you contact support, add your message and any reply. Our guide on the confirmation email explains the first item.