Held royalties, change of company

have interest in a well in Howard County that has been in production since 2010. I have not received any of the royalty payments To date. I finally got Apache to admit their error and a greed to pay me, Back to late 2010. However half of the production Was from early 2010 when mariner energy Held Production. Are they responsible For their half even though they no longer own the well? Is Apache responsible for all with there purchase? I also for some reason thought Apache acquired Mariner. WHAT should be the intrest rate on this production held?