What can I do to get my money back if I was wrongly charged?

I purchased weight loss services. When I called, the lady took my card to hold the appointment and ended up charging me a total of 6 sessions in advance for $1200. Later, she apologized and informed she will give a refund. I used 2 sessions and I did not like the service because the machine burned me and hurt my eyes. I reported this immediately and pursued for the refund. Since I used only 2 sessions, they were supposed to refund me $800 for unused services but did not. They started to avoid me. They went to my back and issued a dispute. They credited the amount but today the bank said they cannot help me obtain my $800 back. I have to go to the police. We did not sign a contract.