I agree...and if the care home manager insists she is given it...tell her if she can't remember her pin or the process of how to get another or phone the bank then clearly she lacks meaningful mental capacity to handle her finances...and just take it over. Let your mum have the battle with the care home if they are not prepared to use strategies to deflect...distract etc. Your mum can't be the first challenging demanding resident they have come across if truly a dementia care home.
My MIL tried the stance of saying that she'll revoke POA with me as attorney when she was in a particular bad mood. All I said was" that's fine when you've sorted it out let me know ". Of course it never got sorted. I tell her my husband and I are in charge and always will be. I agree with other posters your mum has not got capacity to deal with financial services. When MIL was in hospital she could refuse treatment so the doctor said she had capacity. But she could not make any decisions for her long term future. You need to discuss the home's strategy with difficult behaviour. And others are right it's the home's problem with her behaviour. I think you should make a stand over hospital calls as well . My MIL has only been in her home a week and she's had to go for an x ray . No one expected me to go with her. What would happen if you were unavailable?