ADT contract cancelled but they still debiting account

I cancelled my account in 2019 with Fidelity ADT but to date I am receiving email notifications that I am in arrears. when I called I am told that my account was handed over, how when I made the necessary payment to stop and cancel the service? I would suggest people out there shouldn't even try register with ADT, They are ********** who only want to take your money even if you don't want their services anymore. I expect a call back and resolution for my problem