a clause from edcon stating that if someone dies next kin pays even if not married

I had receive a letter from edcon stating my late sister owes them, i called them they requested death certificate, which was sent to them in 2012, i resent the death certificate to them and requested them to close the acc as the person is late, they telling me i need to pay, why would i pay for something i didn't use or sign for? why did they wait 6 years to contact any relatives? Nobody is going to pay for this. Below are the people who are communicating with me via email lucky Nxumalo Poppy Motshele who insist i must pay Tokollo Molekeng Zandile Bianca Mthethwa Diane Mitchell not responded yet but copied in the mail This is really frustrating my sister was single not married, who is supposed to pay for this? Please assist.