Its really tiny and not noticeable. You had to kill something in a small window to claim it.

You should have gotten it if you killed an NPC in the allotted dates after the stream.

In the this news post it tells you how to get it.
https://www.elderscrollsonline.com/en-us/news/post/57557

"For hitting 80,000 concurrent viewers during our Dark Heart of Skyrim global announcement stream, we're giving all ESO players the Long-Winged Bat pet. To qualify, simply log into the game and kill any enemy monster any time between January 16, 2020 at 12:00 AM EST and January 22, 2020 at 11:59 PM EST.

As long as you qualify, you’ll receive your Long-Winged Bat pet by the first week of February. It’ll be added to your Collections automatically."

Check your collections. You don't get a mail or a notification or anything to tell you that you've recieved it, it's just added to the non-combat pet menu.

If you were playing between the 16th and 22nd it's highly likely you will have gotten it. The only time I know of someone who was playing missing a reward like this it was someone in my guild who literally only does crafting dailies and sells stuff in the guild store - they didn't kill anything so they didn't qualify.