ADT Mississauga

I have been a customer of ADT's predecessor Alarm System companies for more than 20 years and have been satisfied with the service. Given that time of loyalty most companies would consider me to be a good customer as I have always paid my invoices on time. I don't recall during that 20 years or more ever finding the need to call and complain about anything.
But since ADT took over it's been a horrendous experience.
For the past 18 months they have been applying my monitoring service payments to the wrong invoices. Then they send me past due notices for the invoices I have already paid.
In May 2018 they finally sent me a message that my account was at zero, then in June send me a past due invoice!
After hours and hours of research on my end, numerous phone calls and many more emails sending proof of bank payment to at least 6 ADT reps, they still don't get it.
There appears to be no internal communication as none of the ADT reps I spoke with appear to know what I have discussed with the others. Each and every conversation with a new ADT rep starts from scratch.
They really need to rewrite their mission statement where they talk about top quality service and putting customers first.
I have since cancelled ADT and switched to Rogers for much better service and a much lower price. I am generally a non complaining person who accepts that we are all human and mistakes do happen, but after 18 months of absolutely horrendous treatment from ADT I will never deal with them again.

September 27, 2018.
I posted this review more than a month ago and received a very nice apology from Madeleine Caron their Executive Escalation representative as noted below. To my surprise I have just received an email from ADT's accounting people saying I owe them $164.08 for an invoice dated May 12, 2017. I've forgotten how may times they change their mind on what invoice is unpaid after I send my bank statements proving payment of every invoice.
It's shocking that one hand of ADT apologizes and closes the issue, and the other hand doesn't know what's going on. This lack of communication with their flawed accounting system has been played over and over for the past 18 months as every ADT representative I speak with has no idea what conversation was held previously with other ADT representatives.
It's absolutely shocking and is just mind boggling how inept their accounting system is. Do yourself a huge favour - do not deal with these people.