Landlord receiving tenant's housing benefit underpaid

I took on a private tenant who paid his deposit and first months rent in advance and subsequently moved in. I then got a letter from the letting agent telling me that the tenant was now on housing benefit but it wouldn't affect payments of rent. My fears came true and he stopped paying his rent. The letting agent chased this up and managed to get the housing benefit paid directly to me. All good apart from the housing benefit was only £109.09pw when the rent I was charging was £115pw. The following month April 2012 the housing benefit paid to me was £94.74 after a review for the new financial year. I was told the tenant had to make up the shortfall. I had and still have got no hope of the tenant paying the shortfall, so I thought I would investigate how much the housing benefit should be.

The property I was renting was 2 bedrooms within Torbay Council.
The LHA rate for a 2bed property is £126.92
I was receiving only £94.74
I am told by the council they cannot tell me how they calculate that figure, but from my understanding the tenant was over 25, living at the property on his own, he was unemployed earning no gross income. So from my understanding there should have been no deductions from the full rental price and I should have been getting the full rental. How can I get the council to check their records if they will not talk to me because of the data protection act? They say it was his benefits, but it's my money! It's so frustrating!

Could someone please give some advice? Thanks in advance