Woolworths account

I paid my grandmother's account through a ATM deposit in june and i happened to put an incorrect ref no. Now they send a message end of june saying the account is not paid. My grandmother when to Woolworths Carnival mall to enquire but they have been sending her from pillar to post. Tryed to call the call center but the account department did not pickup the line. They don't seem to be very helpful at all and the money is in their account. They are suppose to allocate it to the correct account according to my understanding. Yes its not their fault but i expected them to be able to help but now all they say is that there is nothing they can do. We went to the bank they did print out prove that the account is paid but they don't want to accept the prove they say its not valid . so now what do they expect from us? To just let the money hang in their account and we pay again? I don't understand n its frustrating