Payment under P800 is not reflecting in my self assessment account

I was asked to pay an amount under P800 which I paid, next year when I registered for self assessment, HMRC asked me to file last year return also, which I did, but now the payment under self assessment is showing outstaning, but the payment done P800 is not reflecting in my account

Hi,

To review this you will need to contact HMRC:

https://www.gov.uk/government/organisations/hm-revenue-customs/contact/self-assessment

Thank you.