I didn’t know they accepted btc as payment method before. Have you asked them? According to their website you can pay with btc sorry for late reply didn’t check nostr in a while

https://proton.me/support/pay-with-bitcoin 

https://protonvpn.com/support/vpn-bitcoin-payments/ 

 Yes! Maybe they added it back? or Im crazy and was only looking in their phone app. 
 

 Maybe 🤔 I didn’t see the option on my phone app either but haven’t checked the website yet.