Afrihost Cell C just take unused prepaid data as their own if not used!!!!

So I use the top LTE package available from Afrihost and I pay them on time every month if i run out of data I buy the top up as I need all without complaints. So July we had a low data usage month and there was still 50 GB of data left on my cap and low and behold on the 1st August my Data is gone and i now only have my 200GB available to use. My data that I had paid for upfront the previous month is now gone and when I call them they tell me that Cell C doesn't carry the data over so I have no choice but to accept it. This is absolute nonsense and I will be taking it further. How can they take prepaid data and claim it as their own.