Settlement paid but not credited to the creditor.

I hot handed over by Telkom for R360 blake called me and offer me a discount which was R90 off the amount, i agreed to settle which i did on the 29th oct they even sent me paid up letter, i called telkom after 2 days to my surprise i still owe them R90 which means blake did not credit the whole balance, i have sent them emails,requested call backs they just promise to call but nothing, telkom agents says i must provide proof that i received a discounted offer , which i dont have since it was a telephonic convention.