ECSA continue to bill mebership fees after I cancelled my membership.

I have been trying to deregister for 3 years now. It is an impossible task. They continue billing you. When you query them why they continue to bill you it is always the same story: They cannot find your resignation letter. Then you send it all to them again, with all the previous correspondence too. I always ask them to confirm they received it. Then nothing, Come the following you you great invoiced again. How can a society that presents professional people be so useless?