ADT Fidelity Security - cancelled service but still being charged

Dear ADT,

I have cancelled my contract with you in August 2022 and received a confirmation from an Andrea Meyer dated 01 Sept 2022 after numerous e-mails sent, whereby it was confirmed that my service is cancelled.

why are you still Debiting my cheque account? I am unable to contact you, as the line is continuously cut or the operator is so unhelpful.