*****ing from the old and poor

So I'm a pensioner and try to do the right thing. I go to American Swiss Maponya Mall and I ask for the total amount outstanding due to TFG (Sterns Acc) to settle balance owing. The lady helping me gave me the amount to pay, I paid the amount owing in total and abrakadabra I get a call months later asking me to pay R500 owing on the account. My veins were showing as I was screaming at the person on the other end of the line and lo and behold I go back to American Swiss Maponya Mall and was advised the person who helped me gave the owing balance and not the total due. I requested a call to complain and was given ref no. CS-316608 for the call and received a call later telling me that I still need to pay for the shop assistants mistake because I'm old and useless and I can't think and my only income is my pension grant I receive from the government so I now need to make a plan to pay for the nice young lady's mistake.