ProtonMail is not safe. To delete someone's ProtonMail account, just print their email onto some posters, put it up in some public place, take a picture of it and tweet it to ProtonMail. And just like that, the email of your target will be probably deleted.
https://i.imgur.com/d9K9Wdm.png
This is not a service you want to use for anything important. If you have some enemies, they can use this method to ban you.