bad customer service from Direct Axis

i have personal loan with Direct Axis unfortunately my account went to arrears, it was handed over to H P Attorneys, i made arrangements to pay extra R500 towards arrears, i paid that amount over 3 years, with arrears remaining the same (R18,000) yesterday i paid full balance as per settlement letter. now they refused to pay me back all the extra amount which i have been paying. i thought extra money was going reduce arrears but that was not taken into account.

Staff at Direct Axis don't assist, call HP attorneys, they also refused to assist me. what happened to extra amount which i have been paying.