Telkom won't refund even R200

I have a contract with Telkom for data R200 eveyr month since 2012. Previously when the data bundle had depleted during the month I would select add on data and then be billed for this at the end of the month. When attempting to add on data this past month the system for purchase had seemed to change and that now i had to now pay for the add on data beforehand. I was not notified of any changes to my account payment system by telkom. I then proceeded to purchased airtime via the ABSA prepaid service. When inputting the voucher number on the Telkom Self Service page, only then did the message appear that vouchers cannot be redeemed on contracts. There is no where on the page that states this. Only once i had inputted the voucher was the message then displayed and i informed that it cannot be redeemed. I now have a voucher which i have paid R200 for and have not use for. I then contacted Telkom via the live chat service and was told that i cannot receive a refund for the voucher. I was not informed by Telkom of a change to my additional data purcahse system but Telkom are happy with keeping my R200. Bad service Telkom. Really bad. I demand a refund.