Housing Benefit, already paid rent?

Hi

I've got a HA flat, I paid all my rent in advance to mid-July, I didn't realise I could get HB as I was a student but now told I will get it paid from 13th May onwards.

As I've already paid this rent, what can I do with the money? Will the council check that this exact money is going to rent, cos I have already paid it?

I did ask for backdated as I could've got it from the start of renting- I didn't know I could get HB then as a student and lone parent and desperately needed the flat after being homeless so just put all my loan into the rent to secure it. They said they won't backdate cos its not a good enough cause that I didn't know I could get it, saying my uni could've told me. I went to the uni's housing bit when I had nowhere to go and all they did was help put me up as a temporary lodger with my son. I asked then about what I could get and they said no, my loan was to be used for housing? Not sure what to do there, might appeal but hey, at least its paid.

Thanks.