Shabby treatment by ADT/Fidelity Security Services

I previously was a client of AC Security. I terminated my account with them, effective the end of August. As I was in rented accommodation for a while, I did not register for security services with anyone else. At the end of September I received a notice from ADT/ Fidelity in Herm****, welcoming me too the family. I dismissed it as a mistake or some sort of advertising gimmick. Imagine my surprise when a debit order for nearly R300 for ADT went through on my account on the 30 September. I immediately sent them an email asking what was going on. I received a phone call today- Wednesday 3/11/21- from a representative for the company based in Herm****. She informed me that the debit order was because they had taken over AC Security, and as I was a client of AC , I was now their client. I was astounded. I told her I had terminated with AC in August. She seemed to think that I should not be upset with them because it was the fault of AC Security, who had provided them with client details. I pointed out that they had *******ly taken money out of my account , and it was for them to sort this matter out immediately. I then found correspondence via email which confirmed what I had said. I sent this to ADT. I then received a call from someone in the accounts department. Clearly she had not been fully briefed. She again adopted the" blame AC defence" . She then told me I must provide proof of payment, before she could get head office to reemburse me.I told her it was not my responsibility to do anything- they were the ones who ohad taken my money, and they must sort it out, and do so quickly. She indicated she would get back to me by close of business. Needless to say, she did not. I believe that if a company takes over another, the new owners should contact the clients of the previous company and explain fully what has happened. Clients should have the decision as to whether they are happy to stay with the new company, or terminate. there is no way they should simply proceed without any information being provided to the old client. ADT/Fidelity could be doing this to many people. Simply billing everyone who was and had ceased to be a client. It is unacceptable. It is also shabby service that people do not get back to you when they say they will.It is not a matter of the amount of money, it is the principle.