FNB! HOW CAN WE **** YOU OVER! NOT HOW CAN WE HELP YOU

Good day, a transfer was made into my FNB Cheque account via SARS even though stated that i no longer use my FNB account as FNB choose to run bank charges on my account of over R25 000 in access as i was unemployed for 10 months. Instead of the bank calling and trying to assist the customer everymonth the fee's were running up and the account is now in a minues 35000, I called my bank to reverse the money and they advised that the money can not be reversed. Why can a transfer that is made to my bank account in error not be reversed back to the sender? Please can some one from FNB assist me as i have not been working for 10 months my mum has cancer and i need to pay so many people so much money this money was supposed to put food on the table and now the bank is holding the money hostage as they feel this money is their priority due to the account being in arrears. Please can someone assist in trying to reverse the money or even a portion just so i can get my mum her medication and put some food on the table.