Can a motgage co refuse to sign Division Orders?

I leased my minerals to a oil company co. about 4 years ago and received a signing bonus. The property in question is a residential homestead in Texas which I own the mineral rights. The oil co drilled a well that is producing natural gas. They mailed me my division orders in December 2013 requesting me to sign and if I had a mortgage company for them to sign also. I signed and sent to them for over 90 days and finally they sent me a denial letter refusing to sign. I called then asking then there reason and they stated its a new policy they just put into effect stating they were assuming unnecessary liability. Stating a new policy tells me that have signed off on others but not mine. I explained that the oil co. was not physically one the property and they had a pipe one mile under grown running horizontal producing natural gas. To date the oil co. is holding about $4000 that I'm entitled to until the mortgage company sighs off on the division orders. What are my options.