Voucher query

------ I cancel flight last year July and total amount from that reference M8C2KF was R9548. 70.. I apply voucher from that voucher of R9548. 70 I use R3131. 36 for two trips Or Tambo to Durban.. I book another one from Or Tambo to East London I use R1753... My balance was supposed to be R4664. 04...but when I'm trying to book flight call centers agency they told me my balance is R1118... When i asked to check on their system under this reference M8C2KF they told there is nothing.. their system doesn't show anything i have to email my complain to ***... I did but i didn't get any respond ..