Still getting charged for a closed account?

My credit card account was paid up due to settlement and confirmed as closed at the end of March 2016. To my surprise I received a statement saying my balance was R87.23. The breakdown is that I got charged after my account was closed with a service fee of R31. Then also a finance charge of R3.45. Now they tell me I need to pay up the interest on that to amount of R52.78 because they didn't have any instruction to close my card? How is that my fault? I expect this to be reversed and then have this stupid account closed once and for all. This is unacceptable and goes against my consumer rights.