After my first complaint iro Stannic and numerous mails and phone calls I have still not received any feedback or info of my deceased mothers account

After my first complaint iro Stannic and numerous mails and phone calls I have still not received any feedback or info of my deceased mothers account. She passed away on the 12th March, I received the letter of authority (certified) in May and send everything else to them. So once again, 2 months later, still no response. Useless pathetic financial institution