Car track ****

I agreed with car track that I will be downgrading my package they agreed I also paid the fee for downgrading was told that they will send someone to take out my old tracker and install a new one,no came or called then following month they still debit more money and that was not part of the agreement when I ask why they say my old tracker was still there that's why I was charged more So who is at fault and why must I pay for something we agreed I no longer need and also paid their downgrading fees and they didn't come fix