Leasing rights

Well my siblings and I are halfway there, we were involved in the merger from Forrest Oil to Sabine Oil. We still have questions 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 passed in 2001. The production of oil and gas produced in 2002 meant that the lease was still valid. For two, they should have contacted his heirs, and for three, it has been producing ever since. What do we do? We have been in contact with them for years and they are giving us the runaround.