Landlord took hap but with a condition

Hi all going anon for this post.

Last year i moved in to this property i was already hap approved but i told landlord i could take or leave it as it didn't work out a massive saving, the landlord said if at the end of the year the council offered you €1500 or whatever saving in cash you would take it! So i did went through the rigamarole and the first hap month i.e council told me from now pay landlord X great i thought as i had the full rent put away thinking id have extra money towards Christmas stuff.

The landlord turned up during the month and basically told me that the hap is paid in arrears and for me to live here on hap i have to pay an extra full months rent as he doesn't want to be paid on arrears going forward and no one lives in his propertys for free.

Ive always paid my rent on time and my council contributions come directy from my S.W.

When it comes time to move out should the landlord not reimburse me the extra months rent or am I wrong to think that way?

Just to recap in case i missed anything

I paid my first month rent + full deposit out of my own pocket, then got hap and he said he wanted full rent again even though council said i pay the reduced price. I understand he didn't want to be paid in arrears as if i stopped the hap payment he wouldn't know until end of month but this left me out of pocket.

What should i do here?

Thanks