JHK2023

Hi there, I am a non UK resident who owns a UK company, I lent money to the company for business and the company paid me director loan's interest which request me to fill in CT61 form and pay 20% withholding tax to HMRC. I have already filled CT61 form and paid the tax. As the interest shouldn't arise any UK tax due to double taxation treaty between Hong Kong and the UK, I wish to claim repayment of tax. 1) My only UK income was the interests paid by my company. As they shouldn't be subject to any UK tax but still I have already paid withholding tax, do I need to file self assessment? 2) For claiming repayment of tax, which form should I use? I found HS304, R43 and DT-individual forms, which are very similar. 3) While I claim the repayment of tax, do I have to include any reference number so that you can track my previous paid withholding tax? Many thanks.