I believe the word you want is ''deceased''. Debt collectors will never ''get the hint'' on anything. You need to be direct and blunt, and place your demands on paper to make them stick.
I'd guess they think you're hiding Grandma in the closet or else hoping you'll be ever so kind as to pay some ancient debt of hers. Usually debt dies with a person, and any firm looking for a payday has to stand in line and wait for the estate (if any) to call its number ticket. Relatives are not liable. Never mind the death cert, send a cease-comm notice via USPS Certified with card. The FTC and many consumer watchdogs explain how to draft one. Verbal demands cannot be proven, thus are not much obeyed.
While we wait for someone to report a business name, folks, get friendly with the FDCPA, the federal law which regulates collector behavior and provides you simple tools for your own defense. It grants you control of how you are contacted, and the means to sue at low cost. Learn your rights and first response tactics at FTC-dot-gov. See also your state laws for additional support.