My Late husband had a funeral policy with one life but he wrote her sister as a beneficiary

My Late husband had a funeral policy with one life but he wrote her sister as a beneficiary. It was a funeral policy, I buried my husband and I had to use my credit cards to top up. After the funeral I went through my husband's bank statements I picked up one life and phoned them to make a claim. I told them that I was the spouse, I had a letter of authority, executorship from the master of court and there is the Will and Testament but they failed me and paid my sister in law without considering and respecting my husband's wishes. Even after emphasizing that the Will and Testament overrides everything. They made a payout to my sister in law.