As well as a bookkeeping journal I would also keep a phone ledger. Like you, I found utility companies fantastic , LAs Ok and financial institutions dire.
As your mum’s dementia progress you will be more Involved. You will be asked for the same information over and over again and, sometimes, in stressful situations it is hard to think straight.
At the front of the ledger write
Full name, date and place of birth, date of marriage details of Doctor and Hospital?
Make a full list of phone numbers. Utilities, pharmacy, Doctor, Hospitals and Financial institution.
List her medications
Have it with you every time you make a phone call for her . Then list who you spoke to, the date and time, the name of the person dealing with the issue and the outcome.
Promising are often broken or forgotten, but if you can quote dates and names when following up it speeds the process.
If not already said then a mail redirect is essential for keeping on top of any possible financial fraud, believe me it happens, and a track of appointments. It is not fail safe but it will really help. We once turned up at the ‘memory’ clinic to be told that they had phoned mum to cancel the appointment.