I really respect how Mullvad is willing to sacrifice business to give extra security and reliability to the (remaining) customers. I first saw it when they disabled auto-renewal with PayPal, because it'd force them to store PII along with your account. Unfortunately for me, they made one too many sacrifices, and disabled port forwarding[1]. They don't store any contact information that could be used to warn customers…
This situation seems avoidable: what if the payment/signup flow had a big loud warning that you need to configure your own polling of an RSS endpoint using a client capable of pinging you?