I was receiving a discount which Telkom gave me after promise they made about keeping my telephone number when I moved house

For one year I have been battling with Telkom about a 25% discount they agreed to give for changing my Telephone number. From November last year they can't get it right they keep crediting me and then start charging me again.I've dealt with every department including Escalations and they say we don't know how load it on the system after agreeing that yes I was supposed to receive a 25% discount on this account. Please someone help.