FNB- How can we ***** from you?

I have been with FNB over 5 years and sang their praises to everyone I know. I now feel like a disappointed victim. I requested my account to be downgraded in Feb. I was in the branch and sent an email. After that I called the call centre and they assured me it was a savings account. In June I came to realise that I am still being charged as a cheque account which is very infair to me. Then I laid a complaint and they just said sorry and downgraded my account and told me they cant refund me as the account was in use. That is theft! If it was me who owed them even as little as R100. Would they accept a "sorry" from me and move on? No. So why am I expected to be okay with the fact that basically stole from me?