Getting help.

If you know a local radio amateur, with a few years experience of radio, they may well be able to help with advice specific to your situation or even filters at a minimum cost.

If the problem cannot be resolved, you may be able to get help from your local electrical dealer or electronic engineer. They will charge for this service, and will most likely just fit the filter mentioned above - and relieve you of a load of cash for the call-out, time and filter (at their price).
With this in mind, it really is better if you can get it sorted between you and the neighbour.