I've also experienced problems with my mother's doctor. These even pre-date any signs of dementia on her part. The practice overall is not bad, and not uncaring, but it has poor administration and record keeping (IMO), and makes no allowances for the particular problems of the elderly.
At mum's social worker's suggestion, we now try to make sure that either I or my brother accompany mum to the doctor. That way, we can make sure that she tells the doctor what the problem is -- sometimes she forgets why she made the appointment -- and we know what the doctor advised.
To give an example of how the surgery's poor procedures don't help: The last time I attended with mum, she had a cough. The doctor prescribed some antibiotics and told us that if mum still had the cough in a week's time she should go to the hospital for an x-ray. The doctor said that the x-ray department operated a walk-in clinic and all we'd need is a form which we could pick up from the receptionist on the way out.
But when we asked the receptionist for the form, she said it would not be available until the following week, which meant an extra trip to the practice to pick up the form before we went to the hospital.
Then two days later, an appointment for an x-ray arrived in the post, which effectively contradicted what the doctor had said and what the receptionist had said.
This would have totally confused mum, if she was dealing with it on her own, and she probably would not have attended for the x-ray.