[SpaghettiCthulu]

You can pay for VPNs with crytocurrency instead

[cassianoleal]

For Mullvad you can buy gift cards as well. Even if you pay for those with a credit card, there's no link between the payment and the contents of the gift card.

[EasyMark]

I send cash and it has worked just fine. I guess depends on honest mail people between you and them though.