Fees charged after end of membership

I was charged membership fees for 2015 after I ended my membership in 2014. I was also charged interest for 2015 membership fees not paid. I told Sarah Biya that I cancelled last year and she told me it does not reflect on their system. She was forwarded the email that I cancelled membership last year and said this year's fees and interest will be reversed. I paid all my outstanding fees I owed WISA and last week I was sent an invoice for more outstanding fees which I was told would be reversed as I was no longer a member in 2015. I seems as though this will happen yearly from now on and I hope other people will not get involved with this institution because when they decide to leave they will be continuously billed for membership that they do not use. WISA is a member of EthicsSA but I don't see what is ethical by ******ing money from x-members that they don't owe them once they leave.