TELKOM DEVICE OBLIGATION FEE

My contract was due for an upgrade. I did the upgrade and when I received my bill for the month they are charging me a device obligation fee for the previous device because the contract only ended in March. Why offer an upgrade when I still need to pay for the old device? I was not informed of this fee. I upgraded one of my other lines last year and was not charged this fee. When I call to try and resolve this I am told that there is nothing that can be done, because what's done is done. Pathetic service. I have 3 contracts with Telkom and I will be cancelling them all as soon as they come to an end. Absolutely pathetic.