Cancellation of gym membership

I started a gym membership 3 years ago and signed a 2 year agreement. Wich I fullfilled, I then cancelled a few days after my cntract was up. I took the proper steps that where explained to me by ABC Financials representative. 8 moths letter I receive a letter from my bank stating I over drafted on my savings account that is never used.I quickly contacted the bank and they stated that ABC FINANCIAL was automatically drafting a monthly fee. I immedeately contacted ABC FINANCIAL and explained that I cancelled this service 8 months ago. They stated that I did not send them a letter of cancellation! I took the steps that where explined t me and I still got charged for a gym that have not gone to in at least 12 months. I do not understand why I had to send them a letter, when I called them twice and signed there waiver of cancellation! All I want is my $339.04 that was wrongfully billed!!!!! I will tell everybody that will hear me, that this company is a con artist under cover!!!!!!!!!!!!!!!!!!!!