Standard Bank forcing me to keep an account

I have not used my standard bank account in over three years, I went to the branch to request closure of this account, I was told it won't be closed because it has an overdraft. I told the bank I want to arrange for payment for the overdraft & asked if they can close it, they still refused. I asked why my account is not under collections cause it's been sitting on minus for the past 3 years. The account is accumulating lots of interest monthly & I'm now being forced to keep an account I no longer need while Standard Bank keeps charging me for an account that is sitting & gathering dust.