Working From Home Expenses Claim

My son recently tried doing his working from home tax relief for job expenses via https://www.gov.uk/tax-relief-for-employees/working-at-home#:~:text=You%20cannot%20claim%20tax%20relief,of%20coronavirus%20(COVID%2D19) He unfortunately did it for me instead, unaware as we have the same name. I've tried cancelling it but I've found no way at all do so. I've tried contacting 0300 200 3300 as per https://www.gov.uk/government/organisations/hm-revenue-customs/contact/income-tax-enquiries-for-individuals-pensioners-and-employees but it wouldn't let me go through unless it's child benefits or tax credits. Told me to ring 0345 300 3900 instead. So I did that. The woman told me she can't help, and to ask an agent on webchat. I told her it's automatic rather than an agent and it doesn't give me any help at all, yet she insisted it'll let me speak to a webchat agent. I left and tried, but to no avail. I'm no closer to cancelling my claim for tax relief, and apparently being tech savvy hasn't helped one bit, I've skewered where I could to find something that can help, this is my last hope. Any help would be greatly appreciated, so long as I am not forwarded to sites that I've already tried and accessed and asked to call numbers I've already called. Thank you, I hope to receive a response soon.

Hi,
You will need to discuss this with our Income Tax department, all of the contact methods for them are listed here:
Income Tax: general enquiries
Thank you.