Elderly mum being harrassed for deceased sons acc

My brother passed away on 15/04/15, My mum went to Jet - gave them death certificate. Since then, I had to take her on 3 occasions cos they claimed they never received death cert. Now in December my mum went to the store again, and she was told to talk to someone at head office. On the phone she was told that she has to settle the account. Jet never ph & asked my pensionable permission when they opened the acc - y must she b liable to pay? Jet have since handed a deceased person over to some collections agencies whos harassing my mum. I eventually gave them the cemetery address which they gladly took down to send all fwding notices. Is this some joke really? Yet they still phoninh everyday even on the deceased phone and asking to speak to him, saying the call is for a private reason. I dont know what my brothers acc number but will add his id number in the space.