A lot depends on if you still want it.  Only you know that, but since it borders you and you've farmed it a long time, I'll guess that the answer is yes.  That being said, I'd work to repair the relationship.  They made a mistake by getting taken in by a smooth talker and getting excited by their greed.  On the other hand, most of us probably know of situations where the story they were told is true - somebody takes advantage of an absentee landlord for years because of an old relationship.  If you felt your agreement was fair before, I'd suggest sticking to it and figuring that they learned an important lesson.  They now know that they've been treated more than fairly for years, and hopefully that will lead to many more years of business between you. 

My thoughts,

Mike