They sold me a product that doesn't work

They sold me a product that doesn't work. The problem is persistent but Cartrack has not been able to resolve it. Call after call their technical support team instructs me on what to do. I do it and nothing happens. Last week they said they have logged a repair call but days later they have done nothing. And to top it all they double debited me on 1 December. I managed to reverse the second debit order via my banking App. Now that I have cancelled the contract, I have to pay a penalty. I'd rather take this pain than stay as a Cartrack customer. Never again!