Unfairly treatment

I really dont understand how SARS works. You contribute PAYE every month and then they still tell you that you owe SARS. How the heck does that happen. SARS is exploiting people and is seems as if there isn't much we can do about it. You ask a SARS consultant how did you end up owning while you are just ordinary employee, they don't have a straight answer. Allbthey care about is making payment arrangements. How does one really make arrangements while you know you never received any payment from SARS in error and you have been contributing monthly. Nonsense.