Settlement amount problem

i have requested a settlement quotation from Vodacom. as ive done with two or three other companies as well. I received a production bonus and wanted to settle my accounts. Vodacom sent me a quote and i paid it. now two months later, they say im still owing. how can i still owe if i requested a settlement quote. i worked in a financial institution for many years and my understanding of a settlement quotation includes all costs and fees and any other costs. the best answer Vodacom could give me was \THE CANCELLATIONS DEPARTMENT DONT ALWAYS ADD ALL THE COSTS". what nonsense is this and how is this my fault. Vodacom should then tell customers that their settlement quotes are Estimated amounts because their cancellations department has their own unorganised procedures. a settlement quotation according to my understanding is a FULL and FINAL settlement. now Vodacom is doing this. ???? I have the settlement quotation as proof as well as my internet payment. """