poor accounts customer service

i have been trying to upgrade my contract since friday 12 July 2019 and am still having issues with the accounts department having given me incorrect figures to pay and not recording my payments on the system. It is now 17 July and i am still no closer to getting my upgrade. I missed out on a Friday special because of this and i am fast getting annoyed with the service. I now cannot even make a call to customer services because they have rerouted all my calls to collections and it cuts off before i can speak to anyone. I am so frustrated and no one seems to be able to help me, despite my having made numerous payments because each person i speak to gives me a different figure to pay. Please can someone help me urgently.