Posted: Yesterday at 21:02
The Chairman won't be in a position to offer much. Just a person who attends AGMs and such.
Get the name of the Chief Executive.the CEO is in charge of the day to day running of the organisation. Write, recorded delivery (adds to the seriousness), and spell out everything that you have been told and by whom. Name the housing assoc employee who told you whatever they told you and when. Name the independent advice, who said what and when. Enclose photos of the plants and the boundary, including any evidence such as copies of your deed plans.
State that the plants have invaded your property from the housing assoc's property and that they are guilty of causing a nuisance to you and as such would be liable to be served with an injunction.
You then wait. Don't actually set about serving them with an injunction. Wait.