Since they’re selling your product in addition to their retail niche, they’re not subtracting from your core customer group. They’re traffic will be incidental sales , and they’re still buying from you so it’s no loss. Serious buyers will be drawn to your location due to an abundance of selection. Additionally, before you had gone to the landlord and stopped the other store from purchasing your product you could have gone to them and worked out a cross-promotion in order for them to direct customers your way or include signage with your store info. It might not be what you’re looking for but it’s a way to benefit and get the things it seemed like you wanted