You can find more information on housing allowance on the website of the tax authorities. Here you can find whether you are eligible for housing allowance. This benefit is something you arrange with the tax authorities yourself. De Key cannot deduct the allowance from your monthly rent.
The tax authorities calculate the amount of the housing allowance based on your basic rent (or net rent) and certain service cost fees. These fees are the cleaning and energy costs for common areas and the caretaker costs (up to € 12, - per item). The basic rent plus these fees form the so-called "rekenhuur". The tax authorities use the "rekenhuur" to calculate the allowance.
Check your payment history to find the breakdown of your rent.