What should I do about the fact that I was ripped off?

I was ripped off and someone made a mistake and said I could pay now and come back to my martial arts course in one month so I did and I spoke to them this month about it and the woman no longer works in that place and they cannot prove it and neither can I because they weren't there to hear what happened, the other instructors. What should I do about this? Should I insist on getting my eighty dollars back, being on benefits myself and having been ripped off by someone else's mistake, or should I leave it, since I am wanting to continue learning martial arts there for this month and allow the fact that I paid for a lesson that I never received? They've indicated that they can't do much about this except that I should get as much time as I can from them this month which this month's pay includes anyway. I am annoyed about this. Not the money so much as the dishonesty and the fact that I had to pay for someone else's mistake deliberate or not.