Vodacom worst company to take out contracts.

I had 3 contracts with vodacom. I phoned the cancelation department and asked for 2 premature amounts to settle them. They send me the amounts and the forms that I have to fill out to state that it is for the premature cancelation. I paid them the same day and completed the forms. I emailed them back to the cancelation department also on that same day. Then after I did all that they requested they took my full contracts installment from my cancelation money. When I went to the vodacom store to pay my remaining contract they said that I have to pay R1500 on that remaining contract even though the amount is only R440 for the remaining contract. Know how do you get to R1500? Who gave them permission to use the premature payments to pay my bills? I will pay this last contract in full as a premature cancelation and will never do business with them again.