Service fees overcharged and not refunded

I went to Standard Bank Greenstone late December to do enquiries on my savings account. For some reason my service fees on this account seemed to be much higher than normal only to find out that they overcharged me on service fees from July to December. The clerk did the enquiry and had to forward it to the Port Elizabeth branch for further investigation because that was where I originally opened the acc 30 years ago. I then received an email to say that the refund for the monies that was overcharged was going to be approximately R 900. Apparently a Miss Natalie Davids is working on this problem and now only wants to refund me a third of the amount because the is a rule that states that I can only be refunded for three months. I do not see how I have to pay for their incompetence. An instruction had to be sent to the one who works on this acc to rectify as soon as changes was made on the acc. Which mean somebody at the Port Elizabeth branch was not doing what they were suppose to do and still getting paid for it. Still I haven't receive the refund and it is already March.