Got charged twice by eRentersPlan and they insist they only charged me once

I paid renters insurance through a different company (eRentersPlan) until I could get a proper renter's insurance through my existing Auto-Insurance company. They offer prorated refunds, but they double charged me for a year's worth of insurance, which is well over $700. This is not good since I quite literally just moved out and was not able to save as much as I wanted due to circumstances beyond my control.

I called them and they insisted they only charged me once. I was told to send an email with "Proof" in the form of a bank statement. I emailed and the company told me to call one of their agents, and immedietly closed the case without review or reply. I call them again and the agent keeps saying "nOt fRoM wHaT i sEe" as if I'm lying to him, claims there was no case opened, and that I never emailed them, but I'm free to send one to "Prove" I got charged twice. They even threatened to completely cancel my insurance if I did a chargeback on the duplicate charge only.

I send an email, telling them I called ans was told to email. The case is closed immedietly without review or reply.

I'm going with my auto/renter's insurance, and after that's conformed, I'm not even going to ask this third party to refund shit because of these stupid ass games. I'm doing a chargeback. Do they have grounds to sue me for a charge back even though they were only supposed to charge me once?

Location: Texas, USA