Selling the property - lease buyout - foreclosure

We just acquired a 64 acre tract that has a cell tower on the corner. The original landlord sold the lease when he sold the property. The second owner lost all the land through foreclosure. We have been in contact with the cell tower company about the lease. We can not acquire the original lease. They will only send us a Memorandum of Lease. They are telling us they paid the original owner for 50 years and they owe us nothing. If the land was lost to foreclosure does it terminate the lease? Do they need to renegotiate? We are getting no help. They continue to drive on and off our property.