Poor Service

I’ve been receiving the worst service from this service provider.. They failed to debit my account and within the first 2 months I called them to inform them about this but nothing changed and when they visited our estate I went to report this and they said they would fix it be cause their system had no reason as to why I was not debited. So the arrangement was that I can only be able to pay back the money that they did not debit over 12 months. To my surprise they have now decided without consulting me to debit the amount that they failed to debit with no valid reason over 6 months.. And I’ve been trying to resolve this but they are sending me from pillar to post.. please help..