Incorrect billing

i have paid NSFAS as i was ganished i made arrangements to pay in instalments until I finished paying them.<br> from 2011 if im not mistaken. now , im being told that i didnt pay R40.00 Which made interest and now in 2015 im owing them 600. <br> <br> i find it very surprising as i got the confirmation that i had paid the full amount and i have moved offices and cxant find that email. ive emailed , ive used my airtime to recfy this and i was told that they will get back to me untill today I have not received anything from this Organisation