Self Assessment request to pay via employment PAYE

I completed my tax return in August 2023. I ticked the box to pay my tax through my employment PAYE code. I tried to call, I think in January as I could not see any confirmation and had read of others on the forum who had asked the same question. There was no one to take the call with the service currently closed due to tax return deadline. Today, I have come home to an 'overdue' letter, which understandably I am bemused and cross about due to my request on the form. HMRC are shut today! Can anyone offeer any advise why my tick box for PAYE through my employers code has been ignored. Thanks

Hi Kezzy KM,
We are sorry to hear of the frustration caused by your request not having been applied.
This often occurs when we haven't received an estimate of your pay for the upcoming tax year.
We don't want to collect a prohibitively large amount of tax from your wage.
Contact us by webchat or phone here:
Self Assessment: general enquiries
We can either update your code, or offer alternatives.
Thank you. 
 

Wouldn't it be rather useful if information like this was proactively made available to us, either via online FAQs or provided to us in writing INSTEAD OF the generic "you're late paying, here's a penalty" letters we end up getting when something like this happens? Why is it up to us to beg for answers to questions that so many of us are having, and why is the default position of HMRC to assume we're genuine non-payers rather than giving us the benefit of the doubt, especially when you can see we've requested to repay via PAYE, and you then know that you haven't yet received all the information you need from OTHERS - i.e. it's not something WE'VE done wrong - in order to action that request?