Increase in Membership without notification

I went over from Discovery Health to a new medical aid in January and therefore lost my Vitality membership. My Virgin Active membership increased to R250 for my wife and I each. Although this was much more than I paid while being an active gym user and I had not been to the gym for at least 6 months, I still found R250 per month per member acceptable and was willing to pay this amount. At the end of March, however, two debit orders for R500 each (for my wife and my memberships) went off my account and was returned, due to insufficient funds. The cost for the returned debit orders is R125 x 2 = R250. Yesterday I was phoned by the Virgin Active call center informing me to pay R1000 immediately. I said that I wanted my membership cancelled immediately since I cannot afford R1000 for gym fees. I was told that it would be cancelled by 25 April only and that I still need to pay the R1000. This is unacceptable since I was not informed of an increase in membership fees. I insist that my membership be cancelled immediately, that the R250 be credited to my bank account and that a letter be forwarded to my bank as such, since the returned debit order adversely affects my credit record.