On the other hand, if you don't trust Mullvad's assertion that they delete the link between accounts and credit card payment records after 40 days [1], what makes you think you can trust them to not keep a record of individual scratch cards sold on Amazon, which Amazon can then correlate to an order ID and by extension account and shipping address?
At a higher level, if somebody can convince Mullvad to collude in that manner, they can likely also just ask them to outright hand over your traffic flows and connection data.