Double billing

I had device installed on my car in 2014 and in September 2017 I cahnged insurance and contracted Netstar to install a device. I told Netstar that there’s no need to install the new device as there’s already an active device on my vehicle but Netstar insisted saying the Slueth Nano is latest technology based GSM on GSM and recovery is simpler. Devide was then installed in september

To my surprise Netstar is now billing me for 2 devices in the same car, the next minute I’m told the old contract is cancelled but still I receive invoices. Is two months now discussing the same thing with no help at all. Ref ********** .

I cannot be blacklisted for R100 bill and I refuse to give them my money for free as it doesn’t make sense