Leasing rights

Well my slibings and i are halfway there, we were involved in the merger from forrest oil to sabine oil, we still have question concerning royalties payment we also think they are not right.

Now my question is my dad signed a lease with chin exploration in 2000 and he passeed in 2001, the prodution of pil and gas produced in 2002 which meant that the lease for 1 was still valid, for 2 they should have contacted his heirs and for 3 it has been producing every since. What do we do we have been in contact with them for years and they are giving us the run around