Left UK 20 years, still getting taxed ....

Left the UK 20 years ago. Informed HMRC at time. Started my State Pension in 2018 and received tax bill in 2018, 2019 and 2020. Following many letters and phone calls together with submitting a P85 and other forms to take advantage of the tax treaty between UK and US the bills were voided. Then in 2022 I started by private pension and I am now once again getting tax bills. My tax code was changed to NTX in 2023. Have sent in certificate of residence from the US (several), but cannot seem to get through to anyone what I am not a resident and have not been so for 20 years. What else do I do?

Hi heines Dan,
Please note that a P85 is not the correct form for pensions and cannot be used.  
As you are resident in the USA and have commenced receipt of a UK pension, the pension is by default, taxable until we can advise the provider to apply a 'NT' (no tax) tax code, that ensures no tax is deducted from your pension.
To resolve this, we require the DT indiviual form for the USA to be validated by the IRS.
Double Taxation: UK-USA (SI 2002 number 2848) (form US-Individual 2002)
You would need to print off the form and complete it, declaring your pensions, then send it to the IRS (they may charge a fee for this).
The IRS will then send it directly to HMRC, who can then use the validated form to prevent tax being deducted and refund any tax already paid.
If you have already done this, then you can progress chase your form by calling +44 13 5535 9022 from overseas or via webchat at:
Self Assessment: general enquiries
Monday to Friday: 8am to 6pm Closed on Saturdays, Sundays and Bank Holidays).
Thank you. 
 

Hi @HMRC Admin 25, I left UK on 30th aug 2019 and have informed to HMRC over phone and by submitting some online application form. Suddenly I recived a 12 months late penalty notice last week. Penalities total is 300pounds. I tried calling to the helpline but it resulted in vein. Telephone charges from India to UK is huge too. Please help me to resolve this issue

Hi DeviSK,
We would need to access your record to review the penaty charges.
You will need to contact HMRC direct.
There is the option to webchat:
Self Assessment: general enquiries
When you open the link if you click on Ask HMRC online we will check if a webchat adviser is available to chat. 
Thank you.