Refusal to refund

I rented a vehicle online and cancelled before I picked up the vehicle. After about two weeks I requested a refund and I was told the refund had been paid into my account and the proof which I could not read was attached. I got back to them to let them know that the money has not reached my account, I was given the same proof that the refund was paid. I then pressed for the refund and the tune changed, I was told to give them proof that I cancelled my reservation which I unfortunately don’t have as I always delete old emails to save space, it was almost a year since i had been asking for the refund . I explained this on the email that I had deleted old emails and that I didn’t see a need to keep the email as the refund was not denied initially. The last word from Hertz was that since I cannot provide proof that I cancelled my reservation I will not be refunded