Doubel charge on handsets

I'm 19 years with Vodacom, but lately their service is very bad and *****ing money. There is no proudness in the service anymore. I upgraded in May as I have done every 2 years. Now I get invoiced with a double handset charge. I tried to speak to accounts and the only thing I can get from the accounts is that my contract expires in 2 months time and therefor I have to pay for the old handset till that time. This handset was issued in May 2017 and is suppose to be paid up in April 2019 (thats 24 months) and not in end of July - that said they charge you 2 months more for the handset eventhou the handset charge was for only 24 months. I want to know why they tell you, you can upgrade if the handset is not paid up. A person budget if you can afford the new contract, not with an extra charge. I cannot afford this contract anymore VODACOM, I have to hand the handset in to your nearest branch if this is not rectified.