Unfair treatment about my Salary

Fnb took my 12.000 in my Salary Friday on the 14.-08-2020 .when I'm asking them they said I have an overdrawn of 11.900 but they took 12.000 Its not my fault..I've bought furniture in Ok Furniture on the 15-07-2020 they took their money but they made a mistake the money come back in my account .The Fnb did not phoned me alert me about the money .I went there at Fnb and asked them about the balance that I saw in my account Ms Silingela who working there at Fnb said it's my money is available balance it was on the 31-07-2020 when I was there to asked them about the balance my suprised is when they took al my Salary I have debts rents children at home I dont have food for my children So I want you guys to help me bcs is not my mistake is between ok Furniture and Fnb