national letting keep deposits

I rented a property from national letting in cape town.After moving out i have found that they donot payback deposits.Instead they send fictitious invoices from companys with **** addresses. the women in the office handling all of the invoicing is Alta who always says send her a email.Always in a meeting, and the lady who claims to be managing director of national letting south africa just has a atitude of go to a lawyer.After i found what they do i have traced previous tenants of my block and discovered 4 people in exactly the same position.Then after phoning the agent who rented the property to me, she told me that she left the company because she couldnt stand to see people losing out.The estate agent board is going to step in.Hope they look into this before anyone else gets hurt.