Found an interesting legal clause that Proximus must be “affordable”:
§ 2. [¹ Proximus]¹ assure la mise à disposition à un prix abordable en ce qui concerne la connexion, le coût des communications et de la redevance, d'une ligne permettant l'interactivité, en vue de fournir un accès à des réseaux de données, notamment Internet, et répondre ainsi aux besoins particuliers des hôpitaux, écoles et bibliothèques publiques.
(en machine translation)
§2. [¹ Proximus]¹ ensures the provision at an affordable price with respect to connection, cost of communications and royalty, of a line allowing interactivity, with a view to providing access to data networks, including the Internet, and thus meeting the special needs of public hospitals, schools and libraries.
I find no law saying that Proximus must be inclusive. They apparently must serve hospitals, schools, and libraries, but they need not serve individuals. I’ve noticed they give discounts to customers who pay electronically but then withhold those discounts from cash payers.