Billed unfairly

my employment contract expired while i had a contract with Virgin active. i then had a balance to pay on my cancellation of contract. i couldn't pay the amount till beginning of this month (February) when i had money to settlement all the debit. Then went to the branch where i used to gym, a lady assisted me and called a call centre and a lady told me i had to pay a total R3490. i then went to the bank to pay, paid to NBC the whole amount. A day later i received a call that said i have an outstanding amount of R490, which i dont understand because i was to pay the R3490 which i did. now whose fault is it cause at that time i had the money and was prepared to settle the debit. friday i received another call that said i owe R530. I honestly do not understand because i paid already and i was told the amount to pay by a virgin active reprenstative. where am i expected to get that money now? and how is it my fault that their employee gave me an incorret amount while i requested it cause i wanted to be debitfree? i am very upset by this, now i must suffer at the end, how fair is that?