Billing me while on i am still in contract

I am having a contract with cellc took a modern and just renewed and upgraded the contract with them, then two months back, the modern started to give me error messages when I insert it, the message says that I must consult the administrator, then I called the cellc call centre to explain the problem, then they told me to take the device to the nearest cellc shop, it needs the new software to be installed. then last month I took the device to the nearest cellc shop, they booked to be checked and software installation. after one week they sent me sms the quote of R228 in order to install it. then I called the customer centre and ask why do I have to pay while I am still on contract and I just upgraded, they never gave me a clear answer, they just told me that I have to pay that amount because my device's warrant is expired, I fail to understand why they offered me new contract but now tell me that d device is not on warrant. please help, this people are taking advantage on me. it really doesn't make sense, they must install my device for free because I am still in contract with them its even a year.