Social services - abusive neighbour

We live above an elderly couple who have been in a progressively more abusive relationship over the years. Over the past year, the woman has developed some form of dementia but the abuse has continued.
We have always had difficulty knowing how to intervene but it now seems like an official intervention is necessary.
The woman is sick and needs help, not to be beaten by her husband.

Does anyone know what is the appropriate authority in Belgium/Brussels and how this could be raised with them?