Self assessment tax bill

Can someone explain to me how the tax bill is calculated after your self assessment is filled in, I'm very confused. This time last year I filed my 2021/2022 tax return, my tax bill came to £3,000, I notice that HMRC wanted £4,500, to pay for the first half of the following tax year (As I understand to try and prevent people going into tax arrears) So I understand why HMRC does this. The thing I don't understand now is, I've filed my 2022/2023 tax return and my tax bill again is around £3,000 and again HMRC are asking for £4,500, why is this? I've already paid £1,500 from the previous year's tax bill as it was £3,000 and I paid £4,500, I thought I've already effectively paid half of 22/23's tax bill, how comes this £1,500 extra I've paid hasn't been deducted off the latest self assessment return? I'm basically paying double? Surely it should be £3,000, to pay for the second half of the 22/23 tax year and the first half of the 23/24 tax year? Any clarification will be greatly appreciated, thank you.

Hi,

The actual calculation itself does not take into account any payments made direct by you, this is then reflected on your statement. Please submit the return and allow it to update to then view the payment that is required.

Thank you.