i have some dragon protection chants. though i don't remember them fully [i'll mail you] you should, since it's powerful, double up on some things, the pendant you're using, charge it in the moon each night for a month, then on the full moon, pass it through the smoke of some incense designed for protection, and say the chant. meditate with it each day, visualizing a white light entering it.
that being said, you sure it's a demon? how do you know it's not an agry spirit or creature? demons aren't common, but they're easy to figure oout if it's a demon. it will piss it off, but if you've been attacked by it, banish it from your house. a smudge stick works, say a chant like 'all unwanted beings in this dwelling, i cast out, from any door or window, leave forever.' make sure while doing this the doors and windows are all open [if you have a dog or cat that could get out, tie them outside] sprinkle salt on the entrances ways and window panes of your house, wash the floors with a lemon/sea salt/rosemary brew while burning incense for protection. you should pour the water on your doorstep, and sprinkle salt on the bottoms of everyone's shoes.
there are more things you can do, but those are some easy ones to try.