Poor service

I bought a sim card cash in January used it for 1 month, cancelled the sim card on Facebook messenger in February because it was not useful to me i was using another provider for work purposes. Today i contacted Support at Rain only to be told i owe monies because the sim card is still active, how are you even charging my for a sim card i paid cash for, i have again requested a cancellation only to be told by Sthembile to pay the outstanding amount for the sim card to be cancelled which i will not do.