Bad customer service

Hello Peter My name is Henry chelhango, cell ***, I have contracted with Cartrack for more than 4 years my account number is CHEL00019 ,and during these period Cartrack failed to debit my account which resulted into my account to be in arrears,I then made arrangements to pay that account,to my surprise today I received a final demand letter ,which I don’t understand I never failed to honour my arrangements with them ,I called their customer care no explanation ,I’m even told that I can’t spoke to account manager,I felt like joining them was a greatest mistake I ever made in my life , they treat customers like trash