Both The Vampyre and Carmilla are in the public domain. You can download ebooks of them for free using the links below.
The Vampyre; a Tale (Kindle, Apple Books). I also highly recommend this collection by Andrew Barger that includes The Vampyre: The Best Vampire Stories 1800-1849: A Classic Vampire Anthology (Kindle, Apple Books).
Lastly, if you’re into 19th century-set vampire stories, you’re welcome to read my own book, Wallachia, A Penny Dreadful. The prelude, Flowers of Transylvania, is available on Kindle and Apple Books for $2.99. The main story is published as a serial in text and audiobook formats via an app I designed. New chapters come out every few weeks and subscribers get to vote on upcoming story developments as I write them. Download on the App Store.