Dispute of a balance

I have been paying the mentioned company through a garnishee from November 2011. The balance sent to my HR department was for an amount of R18000 and odd. I started paying as from November 2011 and in December i got retrenched and therefore was employed again by the same company as from June 2012 and i then continued paying the account through the garnishee. As per my latest salary advice its showing a balance of R2700 and odd, hence when am calling the company they are telling me that there is still a balance of R18 000 and odd still? I am not willing to pay this ridiculous amount as it is a *******. I do understand that there could be some extra charges on the account but not double the payment. I want this to be updated on my ITC as per the balance reflecting on my payslip because i will not pay another R18000