Incorrect billing and refusal for a credit.

I got a router installed from supersonic mid month August 2024 and the router did work for a whole week because none of the staff knew what was the problem. I must have called more than 10 times with calls lasting over 20 minutes without success. I then asked for a refund for the day it did not work as I had not received their service yet and I was promised I would receive a credit. Up to this day I have received zero cent. And in the last interaction with one of their agent on Facebook they are saying I cannot receive a refund.