There's a wolf transformation in the Epic of Gilgamesh, and as written texts go they don't come any earlier. Although in this case it was a spell cast upon him and he never had a chance to transform back into human form.
There may of course be earlier oral mythology.
The reason the same term was end up using for two creatures, which were very different, was because they were connected. But not in a sense of family ties.
source: pg 800, The Vampire Book: The Encyclopedia of the Undead, J. Gordon Melton
The reason to be believe so was because, the Slavs and Balkans believed that vampire was a stage that came ...
A possible candidate for the story you have in mind is the legend of Lycaon:
In Greek mythology, Lycaon (/laɪˈkeɪɒn/; Greek: Λυκάων) was a king of Arcadia, son of Pelasgus and Meliboea, who, in the most popular version of the myth, tested Zeus by serving him the roasted flesh of his son Nyctimus, in order to see whether Zeus was truly omniscient. In return ...
This may seem odd, but I'm answering my own question. The transliteration answer for (گرگینه) is gorgine. I found the answer here: https://www.wordsense.eu/werewolf/ and the audio pronunciation here: