Why Do I Get Adverts For Dating Sites On Facebook Even Though I Am ‘in A Relationship’?

I am listed as ‘in a relationship’ on facebook, yet it seems like all the adverts I get are about dating sites. Does anyone have any ideas why this could be? I’ve heard their system is meant to be smart and respond to stuff like that. I had ’social moth’ which changed to a dating application but I’ve deleted that now and it’s still the same…