Cancellation

I am disgusted in Discovery Vitality, i have cancelled my membership on 17th February 2015, and sent them an email way in advance to cancel my membership. They had the audacity to double debit my account, after i have instructed them in advance about my cancellation. I keep on getting automated email responses and nobody have called me as my instruction. I refuse to pay bank charges. SOMEONE CALL ME THIS WILL BE THE 6TH EMAIL I WILL BE SENDING. DISGUSTING BAD SERVICE.