wrongfully billed

My account for february was less than usual. After inquiring a bill was send to show i got a discount for service interruptions. This month i got billed double which includes last months account. After making an inquiry they told me that they investigated and found that it was not a telkom fault. But an area fault. And must pay the whole amount for last month and this month. After asking if i can pay the extra amount off because where am i suppose to get the extra money. I was told that i will have to pay no matter what. Some off the times my telkom internet line is not working. And i still get billed for no service for all the days in a month, which is unfair. They made a mistake and i have to pay for it. Are they not suppose to inform you that you must take the discounted amount and keep it aside just in case you need to pay it next month. I feel highly hurt and wronged in making me believe that they are giving me a discount on services that was interrupted. Only making me pay my discount back the next month.