Every day Harassment from Rain call centre

My name is Gcobile Nono Arcina Boyang I have cancelled my rain contract on 3th of April since it was increasing and can’t afford it anymore. I had to pay the amount they said I was supposed to pay for it for the previous month. At that time my rain was blocked since first of April. The router was collected. But I always get calls saying I owe them for April and May how is that possible when they blocked it on the first of April n never used it and the router was cancelled. The harassment I get every day via calls from Rain it’s too much