SIPP contribution, earn above £100k but below the self assessment income threshold

I really hope someone can help me with this. I have applied now 3 times for self assessment since the turn of the tax year. Once in April 2024, once in May 2024 and again today. I have had several calls with HMRC to chase up the application to get my UTR number and each time I have spoken to them I have either been told I will have a response by X date (which has since passed) or that I do not qualify for self assessment and therefore cannot simply fill in an online form to claim back tax relief on SIPP contributions made. Essentially, I have made SIPP contributions to bring my adjusted net income below the £100k threshold and I am due additional tax relief on these payments. How am I meant to apply for this if I keep getting nowhere in applying for self assessment (you don't even get an email confirmation when filling in the form that it has been submitted) to claim tax back and bring my adjusted net income below £100k again? All my other income tax affairs are simply handled via PAYE. What complicates matters further, is that my wife had been claiming tax free childcare, which when I went over the £100k threshold was no longer something we were eligible for, so I specifically made SIPP contributions to lower my adjusted net income below this figure for the prior tax year and stopped applying for it from April, so that the issue did not repeat itself. Any help here would be much appreciated. I am at a loss as to where to turn to next to resolve this matter.

Hi

If you do not need to complete a self assessment tax return, you can still claim tax relief on payments into a SIPP.  
All that is required, is a letter claiming tax relief, broken down to each tax year in question and with supporting evidence, such as confirmation of payments from the pension provider.

Thanks