The flipside of requiring a provider to submit paperwork to terminate your service, is the situation where in order to setup a new server with DO you'd have to file paperwork yourself. Can you imagine sending a paper letter every time you need to spin up a VM?

Which one do you prefer? paperwork in both directions or no paperwork?

Email is legal in all countries, as far as I'm aware.

I used to work for a SaaS firm. Every once in awhile the main office would receive a written and signed letters from (primarily) German users when they wanted to terminate their service. (We accepted that after confirmation using an authenticated email address, of course.)