ADT trying to ****** money from a pensioner

On 10 January 2023, my mom went to ADT Polokwane to cancel her ADT services they gave her a form of which she filled in and the lady assisting her made a copy and gave her a copy to leave with. The reasons for her cancellation was that they had failed to come replace the battery of their equipment despite having reported the issue to them multiple times. But were busy debiting her account without delivering on the service they promised.

Months after she cancelled their services ADT sends her an sms saying she owes R2086.55, we engage ADT via email speaking to a lady called Khosi explaining to her that the account was closed on the 10 January 2023, we further even emailed her the forms my mom filled filling for cancellation of service. They say they are investigating then they start harassing my mom with phones calls. I have asked that they provide the basis of which my mom is owing and they have failed. My mom is a pensioner who has retired more than 5 years now and they keep trying to ****** money from her. We have proof that they had debited her account multiple times even after she canceled their services and that her account wasn't in arrears even when she cancelled.