Unceremonious Bank Charges

I have a Target Investment account for about 2 years. A minimum deposit allowed is R100 pm at a small interest when withdrawing. I have been depositing and withdrawing at far less than R15 at a time. I was shocked to find that about R97 interest was charged to my account. On enquiry an official at Key West mall said that it recently increased / introduced. No one before communicated that to me. Whenever banks increase fees we're always told but not now.