Cancelled account from two years ago

I app**** for a rain sim card back in 2021, received the sim card and the network had not been registered in the town where I was living. I cancelled the sim through the rain website and I only paid one monthly installment and later had to pay the cancelation fee. Fast forward two years I get a call from Rain stating I owe R309.03c on my Rain account. I logged into my rain account and discover that I infact to owe them that amount as they claim. I don't pay anything before I do some investigation, and I went through my payments on the Rain website and see that I have in fact paid the amount due. I am very confused firstly as to how they discover after two years that I owe them money and also that I have in fact paid the amount, so what exactly do these people want from me?