Self assessment higher than it should be.

I feel a fool but it's become apparent that last year and this year tax bill has been roughly 50% higher than they should be. I earn roughly £17k, last year's tax bill was 1600 with a 700 advance, and another advance in July. Fair enough. BUT neither of those advances have been reflected in this year's bill! I'm yet again asked to pay the full whack of £1700 AND another £800 advance for next year! At this point the advance are a robbing, there not being deducted from the account after self assessment. And yes I did wait 72 hours for this year self assessment to register. I can't afford to pay over the odds for my tax. I just want to pay want a owe. These advances are going to drive me into debt.

Hi Sam Chapman,
Once your tax return has been completely filed, any payments on account made should automatically be deducted from your overall balancing payment.
Please contact us by webchat or phone here:
Self Assessment: general enquiries
To allow us to review your record and confirm your balance.
Thank you. 

I've found my ACTUAL tax bill. So this is feedback. The calculation lacks deductions from advance payments, this is confusing. It either needs to just tell you the whole years tax without any advances OR gives the years tax bill with advances AND deductions. Having just advances on there is Hella confusing. Finding the ACTUAL tax bills to be paid wasn't easy to find. Under the 'pay' clickable link I could have chosen any amount, rather useless when you can't see or haven't found your actual bill. I eventually found what I owed by 'clicking around' and all the hyperlinks and found what I owed plus next year's advance with all deductions from previous advances. Feedback. Either how the calculations is shown should not include advances OR should include them while minusing last year advances. After the calculation, there should be a clearer way to find out how is owed for this bill period (January) instead of dropping you out into your account with rather vaguely names hyperlinks.