I'm sorry, but you seem to have misunderstood my situation. This is not multiplie contacts, but multiple associated google accounts to the same contact:
In the contacts, there's the "Myself" entry. This looks normal on first sight, but when I go to edit it, there's one tab with the contacs information that is stored on the phone, and then there is tabs with the gmail address. The problem is that there's not one, but (I recounted) more like a hundred of them, all with the same info (mail address and name). There's a button to "Unlink contact", but apparently there being so many of them, using the button and clicking "Done" is too much work for the contacts app (not responding, I gave up after "wait"ing four times).
Going through google.com/contacts does not help, as I have moved all contacts to phone storage.
does not detect the duplicate tabs, probably because they're not seperate contacts.
I will try contacts+ as per your reccomendation, though.
EDIT: nope, contacts+ dos not even display the "Myself" entry, so no chance to edit it through that one.