Someone else has access to my account!!!!

I opened a business account 4 months ago at standard bank Malvern branch. For 2 months in a row now a debit order from African Bank keeps coming off my account for the amount of R882-02. I found out that another person has the same account number as mine. Now I have to suffer as his debits are coming off my account. I phoned the customer care line today only to be told they can only assist me on Monday when my business banker is at work. I want to know how can a mistake like this be made as this is my business money that another person has access to?????? This person even has signing power on my account!!!!! It is disgusting that this matter cannot be resolved immediately. This person can draw my money whenever he wants to!!!! I had my previous business account with standard bank for 12 years and this has been the final straw!! So disgusting that they can make such a mistake as they call it!!!! Going to go to my lawyers to see what I can do about this!!!