account number allocated to 2 different people

I had a savings account with standard bank for many years account number ***,i therefore moved to another bank and my account was no longer active but I did not close the account as it was listed to my contacts and creditors.i subsequently enquired with Gems why my contribution savings where still outstanding and Gems advised me that this was paid on the 14 may 2015 to my std bank account and I went to enquire at std bank only to find that the account that used to be mine belonged to someone else and the money from gems is in that account, so now I'm confused as to how is this possible that 2 different people be allocated the same account number, all I want is my money from gems and all the other monies that was intended for me that went to that account which used to belong to me.<br>