Declaring Charity donation for previous tax years

Hi I have been trying to find a way of declaring charity donations for previous years. I have done this in the past by simply writing a leter but this year it was rejected. I have applied to fill a self assessment form in but this was also rejected. I have found a mechanism to do it for this or next year on the website but not for previous. I have also opened a SIPPs I would like to declare but have had similar problems. Any help appreciated!

Hi ,
 

We would need to access your record to see why the declaration was rejected. You can contact HMRC at : Income Tax: general enquiries  . Thank you .