a banishing is what you need. though i don't know of any strong ones [i should though] couple it with a cleansing and protection spell. it'll be a long process, but it should work. what you should get is sage smudge, rosemary, sea salt, and lemon juice. first, mix the rosemary [7 springs] with 1/2 cup sea salt, 1/2 cup lemon juice, and 7 cups of warm water in a bucket [if you wish to heat it on a stove you can, but this is quicker] use this to wash everything in your home like furniture and floors, but especially doors and windows. speaking of, they should be open while you do this, and be sure you chant something like 'wash away the darkness, replace it with light, all evil leave my home' while visualizing a white light washing away negative energy as you clean. be sure when you sweep/wash your floor you do it in a circular motion from the middle out. if you have carpets, just sprinkle the sea salt over them and vacuum it, but do so from the middle out, and while chanting/visualizing.
next get some sage smudge and burn it, wafting the smoke into every inch of your home [in corners, on the ceiling, behind book shelves, around doors and windows] while visualizing and chanting. after you sage a room, be sure to shut the windows and doors behind you.
once you finish that, create a protection charm for you, each person in the family, and the house to keep it from coming back. if it does, i've read in Scott Cunninghams book Earth Magick [i think it was that one anyway] make a black mirror, place it in the upper corner of the room where the spirit typically dwells [at at 45 degree angle would be best] visualize/feel the energy swirling counterclockwise through the room and into the mirror. if you feel there's still some left, you can repeat this a few more times. once you feel it's all inside, draw an equal armed cross [a + sign symbolizing the four directions/elements start at the top and make a straight line down with the forefinger of your power hand, then from left to right.] on the mirror trapping it in a different area far away from your home. leave the mirror untouched for a week, then clean it with either vinegar or an ammonia solution to get rid of all negativity.