npm erased Plesk 12 on Ubuntu 16.04
First of all, I recommend to change the hosting provider, as their answer is incorrect and it seems, that they don't have much experience with Plesk, nor do they seem to have much knowledge about Plesk.
Second, your statements are a bit unclear, as you state:
although I made a backup
and directly afterwards you stated:
and I didn't
Could you pls. clarify WHAT you did and what you forgot to do?
Third, pls. have a look at => "/var/lib/psa/dumps" and inform us about the possible content.
Fourth, if you have dumps located at "/var/lib/psa/dumps", you will always have the choice to re-install Plesk and to re-import the latest "psa", "mysql" and "horde" - databases from your dumps. How to restore a Plesk database dump is explained at:
=> https://support.plesk.com/hc/en-us/articles/213904125
If you have further Plesk related questions, I recommend a new thread at the official Plesk Community Forum ( => https://talk.plesk.com ) , where experienced Plesk users will help you with Plesk - related questions/issues/errors/problems! ;-)