Here are some old time remedies for deterring spirit visitations.
Place rock salt crystals on window sills and beside doors.
Supernatural: Power of Salt To Ward Protect Against Spirits
Sage smudging using dried white sage leaves
Smudging at SpiritDiscovery.com
These are just self help suggestions which might work, or at least make you feel that you are doing something constructive to remedy the problem. (There is nothing worse than the negative feeling of helplessness to exacerbate the problem)
The smudging methods suggest using a mini 'torch' but I find that a twig with a few leaves stuck upright in a blob of blue tack on a porcelain plate will do (less of a fire risk)