Self Assessment of Property Rental Income - No UTR Number

Dear HMRC, I'm a non-UK resident and stayed in Hong Kong. I purchased a house last year in the UK and rented it out to get the rental income for the financial year 2023-2024. For self-assessment purposes, I mailed the NR1 and SA1 forms to HMRC by the end of March 2024 but I did not receive any mail or email from HMRC with the UTR number and activation code for online self-assessment submission. How can I contact HMRC to obtain the UTR number and activation code?

Hi KAMWING So,
You would need to contact our self assesment helpline on 0300 200 3310, from overseas +44 161 931 9070 (Opening times: Monday to Friday: 8am to 6pm Closed on weekends and bank holidays) or contact our webchat facility at Contact HMRC (Opening times: Monday to Friday: 8am to 6pm Closed on weekends and bank holidays).
Thank you.