Unauthorised charges after settling outstanding bill

I have received nothing but a shocking experience with your collections department. I was called in August to advise that my account has been handed over, paid and settled the account in September. The consultant who called me never mentioned that the call will attract a fee and I advised them not to call me further since i will be settling this account at the end of the month. To my surprise, now 3 months later I'm called and advised that the collections department has an outstanding amount of R135.00 I refuse to pay that amount because when I was informed of the outstanding balance, I committed to make a payment and requested that no further calls should be made to myself and my husband. If this is a way for your company to make money, its ********* and will make you loose customers. How can one call that did not even last 3 minutes amount to R135????? Please can this be sorted out and resolved asap. These threatening calls are a nuisance and unnecessary