They refuse to reverse my money from their account

I had a loan with Capitec and due to financial reasons I could not make any payment of the loan for a period of 4 Months capitec handed my account to vertex solutions and I was paying the loan through them. In November 2015 I requested a settlement amount of which I failed to pay the whole amount I just paid my normal installment, again in December I requested a settlement amount only to find out that they increased the amount by almost a R1000. I settled the whole amount on the 16th December 2015 then on Friday the 18th they debited my account by R2000 I called numerous times before I was assisted by someone from enquiries names faith she told me that there's only one person working in the finance department therefore the person has too much work hence I must go to the bank and reverse my money. I told her they must reverse it because they deducted it, why must I be charged for their sloppiness. Can they please reverse my money because I am still awaiting their feedback on when they planning on reversing it.