TERRIBLE Customer Service, lies all around

For the past few days I have been trying to query my contract invoice. I have been promised call backs, and told that is not their department, being told that I'm being transferred to the correct department only for my call to be dropped. I am signed up for a 36month contract, with the initial Invoice/quotation stating that I would have a 36month discount, now the discount is all on a sudden removed, and nobody wants to assist.