You are entitled to a refund. Don't waste another second speaking with F9.

1. Initiate a chargeback with your credit card issuer (bank).
2. File a DOT complaint.

With both, supply a copy of your e-ticket, receipt, the schedule changes, your request for a refund, and the denial.

For the benefit of others, you are going to find out quickly whether you are getting a refund. When you are denied or more than 7 days have passed since your request and no refund has been initiated, move to chargeback + DOT on the 8th day. Do everything in writing and keep copies (screen shots are fine). Supply that paperwork with your chargeback + DOT complaint and you will find this resolved in your favor fairly quickly and without a time investment on your part.