Don’t know what they’re doing

So even after receiving a cancellation certificate and an email from the collections department as to what is the amount that i should be paying to settle this accounts, I receive another invoiced that was invoiced to my account. How can they continue billing even after the tracking device has also been supposedly deactivated. I have never received such bad service in my life!!!! Wonder how long this will take to get resolved and they better know I will not be paying for this invoice,this is just ridiculous so tired of this horrible service honestly!!