Illegally placed bollards on the highway

I spoke to a lady last week concerning this issue and was asked to send in a photo to enable you to send a letter to the person concerned. This has been an ongoing problem for a very long time where the owners of number 50 constantly place a bollard outside their house to prevent anybody parking there. My mother lives and owns no 48 and they have placed this at times over the front of my mother's house which as I know you cannot and shouldn't be doing therefore this has caused him to become verbally abusive to me when I removed and explained why ! I don't want this to cause my mother any further stress as we have already had to deal with other issues via a solitor.