Malfunctioning battery on wifi device.

I have two data wifi devices, both on contract with vodacom. Last year one of these devices, the battery started to swell, battery cover would not close, would not charge and was heating up. I report this device to vodacom and they took in the device and advised me that i should receive a response within three weeks. A month later and no feedback and i complained on Hellopeter and then i received response with my device being sorted out without a charge. Now i am having the exact same problem with my other device and on Saturday(30th March) i handed the device to Vodacom Repairs Umhlanga Ridge and the staff there advised me that my device is under warranty and they will sort it out within three business days. This afternoon i receive a call from a rude lady from the vodacom repairs department stating that there is a charge to replace the battery on the device. I explained to this lady nicely, that i had a similar problem with other device and vodacom sorted this out without charging me. She did not listen to me and insisted that the device battery has a six month warranty and thereafter i need to pay. When i advised her that i will lodge a complaint, she said "no problem, i can just come and collect my device". How Rude!! Wheres the customer sevice provided by vodacom. No apology etc. How is it the customers fault that battery on vodacom device is malfunctioning, not just one device, both of my devices of which i still paying for. This is very poor service provided by vodacom.