Lost the updated contents of DOC-file, which was supposed to be saved (did not close it without save or delete it)

You mean that you left the doc open for two days, and didn't shutdown or restart the PC in that time?

Was file History turned on?

In file explorer you locate that file/doc, Rt Click>Properties>Versions, any shown?

No, I did close the file (it didn't ask me if I wanna save the document as I always do it by myself before closing the doc), shut down the pc that day. Yesterday didn't open the file. Only today opened it and found out there's nothing.

Yeah, nothing, no versions shown

Are you sure that you the manual saves were successful? Where is/was the document stored? On the local computer? On a network drive?

If you found an *.asd file (AutoRecover file), try opening it from within Word, via File > Open > Browse. Note that some users have reported that you must move the *.asd file into the UnsavedFiles folder first (this is the location where Word puts unsaved copies of documents, and you should be able to search for it in File Explorer if you make sure to display hidden and system files first).

Now I’m not sure my manual saves actually worked...But I was doing a lot of those saves within the document all along several hours of writing - and nothing worked which is rare. 

I have this file (in form which I previously created it) on my local computer, but there’s no .asd file, only a huge .fsd (“failed to save document”) file. 

If the fsd file is not too large to attach to an email message, send me a copy of it that way, referencing this thread in the covering email message and I will see if I can recover your document.

Alternatively, upload a copy of it to the following folder of my OneDrive

https://1drv.ms/f/s!AmuIXmFDy-1a8nP3RpgnYHp-5zXK

and send me an email to the address shown in my signature to let me know that it is there.