Virgin Active Cancellation

Good day, Heinrich here. Today I have cancelled my gym membership at Virgin Active Gants in Somerset West, after 2 years with my contract the contract went from R467 to R500 month to month because my 2 year term has expired. When I was there I am apparently liable for the remaining debit of 40% for the NEXT debit of the next month, the next debit order will deduct R276 (which is not 40% btw). I explained to them that gym membership fees are paid in advance why should I be liable for "40%" of my month to month contract ? He did however told me that I must cancel my membership within 20 (business) days before the next debit which is basically almost a month notice. Anyway, I can gym till the 17th May, that's not what I want, I want it to be cancelled, it sounds to me quite suspicious to force someone to gym and force to take their money. Long story short, I have put a block at my bank to stop any future debits from Virgin. This is ****************, any suggestions or help on this, what must I do ? Was putting a stop at my bank the right thing to do ?