Refuse to pay out money that was claimed

My late Father passed away back in January 2021. He was working for DSV. DSV did their part just in terms of paying out all that they were supposed to pay out of the funeral arrangement money and all even though they dragged the entire process because we got the money long after the funeral took place. Thereafter we were told to claim the rest of the money from Fairheads Benefit Services as his case was handed over to them. I'm 18 now... legally I supposed to get the entire money instead of getting monthly payments. Even the monthly payments that we were supposed to get me and mt sister... we used to get in drips and draps as some months they wouldn't give us. We claimed already and i was supposed to get the money we claimed for back in March. They have been purposely dragging the process for months now coming up with different excuses on why they can't pay out. Please Help.