Hi Mar Sam,
1. The payments on account are not shown on the Self Assessment tax calculation, SA302. The credit for the payments on account made are shown on your statement. The payments on account will be deducted from the balance calculated on the SA302 with the difference being due for payment.
2. If your self employment has ceased this will not automatically close your Self Assessment. You can check if you meet Self Assessment criteria at
Check if you need to send a Self Assessment tax return and if you do not you can send a submission to close your record. Once closed the 2023/24 payments on account will be cancelled.
Thank you.