Overbilled

I have received a bill stating that i owe the city of Tshwane an amount of R1400.00 for my electricity. My bill is usually between R150 and R300 and now i was told that they estimate and i wasn't billed for 2 whole months. I was unaware that i was not billed. However even if i wasn't billed for those two months how is it possible that the bill amounts to R1400 for 2 months whereas i usually pay anything between 150 and 300. I went to the complaints department and i was told i need to pay the full amount or else they will discount my electricity. I mean it is the municipalities fault that i was not billed, they should come up with an arrangement on how we can pay the bill. I mean where on earth am i supposed to come up with that amount of money in a few days.