Cancellations Overcharge!

I have 3 months left of my contract and requested to prematurely cancel my contract as they are too expensive.<br> Vodacom promised that I would only need to pay 75% of my outstanding balance. R405 X 3months is R1215 right? I paid 75% of this which is R911.25, now saying that I should pay R1102.59. How on earth do I basically pay full price for a service that I would even be using for 3months? On top of it all, false advice to clients saying that 75% is due? I've been a client for very long and disappointed that this is happening, all the agent can say that this is 75%, its system generated, any person using a calculator can see this is not the case!