P800s and simple assessments

Hi, I've not yet received a P800 for TY23/24 although I know I have tax to pay on savings interest during that year. When is the latest that these will be sent out or do I need to call HMRC to ask for it to be done? I have an online account and it says tax not yet calculated for that year. Also, my mother has not yet received her simple assessment and is waiting to pay the tax on her pension income. She does not have an online account as she is unable to verify her identity so can't check that way, We both know we have tax to pay and would like to settle it as soon as possible. It's very frustrating, as the guidance for both situations states that HMRC will contact us with the calculations but it's getting close to the deadline so should we be contacting HMRC by phone instead? Any help would be appreciated. We just want to pay our tax!! Thanks.

Hi,
While not receiving a P800 may indicate that you have no tax to pay, if you believe that you do, please contact our Income Tax team so we can provide you with an update. 
Income Tax: general enquiries
Please note, you and your mother will need to contact us seperately to discuss your individual records.
Thank you.