Very bad service

My name is Polite Thwala my contact number is ***. I would like to report a very bad service received from First National Bank and Capitec bank. i am suffering a lost of R4500. i transferred money from my capitec to my FNB account and in error i used my old account number with FNB. i realized a month later that i used my old account number with FNB. i then requested capitec to assist recall the money Capitec came back and said the money cannot be reversed as it went through an active FNB account. I went to check with FNB i was told that my old account number has been recycled and is being used by another person/ business account and the money went into that account. i want to know how does the bank recycle bank accounts. i want my money back.