Is it possible some of the boarder's are frozen? If your horses are frozen, they do not count towards income for boarding centers.

I'm mostly just confused what you mean because boarding centers are foe upgraded players and you are basic. Unless this is a side account? 

I set it up while I had a bronze account so it never went away 

THANK YOU dusty angel they were frozen

Can you still even run it after you are no longer upgraded? I would figure it would close

It weirdly enough does since I have people in it I think?

You need to report this as a bug, you should lose access to your boarding center and all horses automatically kicked as soon as your subscription ends and you go back to a basic account. 

Thats what I thought. Horses are usually kicked when someone downgrades so I didnt think you should still be getting anything from it. It may count as explotation, so you may wanna be sure you report it.