Being difficult

My mother passed away on the 21st of January 2023. I was phoned by Sentinel and told I will receive a last payment of the mine pension. I phoned them again on the 10th of February, after I forwarded her last will from FNB bank and required paperwork to them, only to be told who is the Trustee? I am her son and why all of a sudden is this now a issue? Still now payment.