Hi Kwok Ching Tsui,
If the company has been dissolved at Companies House, there will be no filing requirement for a CT600 Corporation Tax return.
Dissolved companies no longer have any filing obligations as the company record will no longer exist.
If the letter is addressing that you will need to file a SelfAssessment tax return, this would be for the individual and not for the limited company.
You would need to contact the Self-Assessment helpline to discuss this query.
Self Assessment: general enquiries
Thank you.