Reported gain online in 2022, still waiting for purchase reference

I reported a CGT last year and am still waiting for my online payment reference. https://www.tax.service.gov.uk/track shows my form stuck at 'Received 12 Dec 2023'. The website says it should only take 15 days, and the 'Check when you can expect a reply from HMRC' link doesn't support capital gains. It's a straightforward stock sale (similar to one I reported last year and got a payment reference in the expected 15 days for). How do I get 'unstuck'?

Correction: Typo in the title. It should read 'payment reference' not 'purchase reference'.

Hi,
We would suggest that you contact our PAYE helpline 0300 200 3300 or via webchat at:
Income Tax: general enquiries.  
If you have exceeded the 60 day period for reporting and paying this tax you can appeal the penalties and object to any interest.
Thank you.