Student loan received less than I thought and given priciest accommodation

I am starting University in September and I was told I would receive the maximum loan because I am from a single parent family and my mum is on a low income. I have been told I am entitled to 500 less than originally quoted.
I have recently been ask to add more information to my application such as my NI number, could this change the final sum once the application is complete?

Thanks for any info