Is my landlord guilty of harrassment?

[smileysun]

My landlord has let the neighbour concrete over part of our garden behind our fence (it is our garden) even though we have objected and there is no reason for it. The small piece of land was left as a 'buffer' zone between us and our neighbours as we do not get on and this was done as per a previous agreement with the landlord and their surveyor. They are not responding to calls, letter etc. And they are failing to protect us from harrassment and now seem to be harrassing us themselves! HA is the landlord.