I was dumb enough to buy more than 30 days worth of mullvad once. They changed their terms of service to remove port forwarding. Because I'd paid more than 30 days ago, they wouldn't refund me anything.
Screw mullvad. I'd have to be a damned fool to to ever trust them again.
I don't hold it against them, but I got burned by that change too; but it was entirely reasonable, allowing inbound provides abuse opportunities which degrade their primary service reputation.
I wouldn't be mad, had they have been willing to refund since they changed the functionality.