Failure to send a debit order instruction by the accounts department

I have been paying this service provider or company for a number of years, and I have had the worst service from Fidelity ADT! I changed the banks and notified the service provider or company, and they were able to debit the new bank for two months or so. I was surprised when I received a letter from their internal legal team. I then wrote a letter to them, raising my concerns regarding their failure to send debit order instructions to my bank, and to date, no one has ever rep**** to my letter.