How to get my passed mother's money from the bank?

How to get my mother's money from the Bank which does not accept her WILL and document sign in Bank in case of her passing away?

Go to court.

A will - that is the document your mother signed - needs to go through a court process called probate. After it goes through probate you can claim your inheritance and the money in your mother's bank account. Probate in Poland is not quite the same process as in the UK (or perhaps America) but they do have a way of ratifying the will.

You can immediately withdraw the money only on condition you are the co-owner of the account. The other way is to withdraw it step by step from ATMs with a debit card until the bank learns about the account holder`s death and blocks the access to it. .

If you were only authorised by your mom to use the account, it is not enough for the bank when it learnt about her death. They need the court ruling.