How do I delete a follower who does not show up on my follower l

How do I delete a follower who does not show up on my follower l

For about a year now someone, now a level 67 has been following my farm as a ghost. What I mean by this is he or she does not show up on my follower list ...all followers are found and accounted for,but this farm is not. I wish to delete this farm but can not.
It is a working farming selling and constantly ,constantly ,constantly, constantly buying from me. At one point about 8 months ago he or she healed my blackberry bush, and they showed up in the last helpers box/list, I immediately added him or her to my friend list but recently deleted them thinking I'd get rid of this unwanted follower but they still constantly buying up my slots. I' m a level 118 and would like my 500+ followers to be able to buy from me and also add new followers. How is it possible for someone to " follow " my farm but not show up on my follower list? As I said before, all other followers are accounted for ( I've actually counted ) I'm tired of this " ghost " and want to be rid of this farm calling themselves " Lakers " and now a level 67 ! Please reply soon, I need your advice.