Poor service in this Gym

I have been struggling to cancel my membership since from last year August, I have sent emails to East rand mall gym company informing them that I want to cancel my contract and they have not bothered to cancel it. After 4 months that's when they send me what'sapp messages telling me am in errears have to pay them and I tell this lady her name is Nomfundo and even show her the email I have sent that am canceling my contract. She made calculations for me that I have to pay for in order for them to cancel my contract and also pay the errears. What I want to know is why must I pay errears as if I didn't inform them in time that am canceling my membership it's not my problem that they are not doing they're job. Am willing to pay for the cancelation fee but not the errears. Thank you Zandile Grace Mavimbela