Mines hardly anything, but when i put my accounts in in april i'm going to get hammered because of this payment on account, or the fact that you don't pay anything for the first year.
My first year was a standing start and i had high start up costs so little was due.The tax partnership i left mean't that she(my wife) got clobbered with a bill this jan similar to yours although i phoned them and have been paying by direct debit before it becomes due.
They have guessed my tax to be the same this year ( which it isn't) and then they will want much higher payments on account too, so once again in jan i am going to ask for an arrangement even though i don't declare untill april.
When you have steadied after about three years your tax reflects your earnings, before that it's either nothing or a lot.