I recently closed an account with Viasat and was told I owe for the entire month because I closed 2days after the new cycle and they don't prorate

I spoke to a rep and was told I owe for the entire month of March because I called and discontinued my service on the 1st instead of the 28th. I also tried to set up a payment plan and was told if I did not pay the balance in full it would be turned over to collections. When I asked to speak to a supervisor I was denied and the rep told me its company policy not to let me talk to a supervisor. What can I do?