Deputyship for mother incurring penalties

Hi my mum has dementia and was put into a care home two years ago, since then i have been trying to get a deputyship to handle her financial affairs, which i finally managed last month. I submitted a tax return for her a few months back (she only has a minimal rental income) but im getting constant penalty notices. Trying to call the helpline always puts me in a loop and points me at online resources (not relevant) then kicks me off. At some point she registered a tax account but obviously we have lost access. I suppose just asking if anyone has any advice on this?

Hi Thumpa28.
If you have authority on your mother's record to act on her behalf, contact us by webchat here:
Self Assessment: general enquiries
So we should be able to advise you further.
Thank you.