Unpaid death benefit poor service

My late sister had a policy and my dad is one of the beneficiary's which they are refusing to pay. My dad had 3 names and one of them is not on his ID and it's the one listed on the policy. I have sent countless evidence and documents to prove that they are 1 and the same person but Liberty is taking me for a run around. I have send marriage certificates, his ID, death certificate, my mom's affidavit proving that he is my late sisters father. They even asked for a birth certificate for someone born in 1981 knowing very well that old birth certificates don't have parents names. They are doing everything in the power not to pay my dad's claim. Shame on Liberty for very poor service. My sister never missed a single debit order and this is how you repay your clients?