Fed up

So, I complained about the lack of communication and got a phone call shortly after that. I discussed my issue with the lady that called and we came to an agreement that I would only pay a certain amount as she had credited me with the difference. I paid the amount agreed upon and so help me I get an SMS today to say there is a balance still outstanding on my account. That balance is the credit that should have been passed on my account. A total lack of communication within the organisation.