Your council should send a written decision explaining why your Housing Benefit claim was refused. You can ask the council to revise or reconsider it and, if you still disagree, appeal to the First-tier Tribunal, normally within one month of the decision date. While this is being dealt with, keep paying what rent you can and speak to your landlord if you are worried about arrears. You may also be able to apply for a Discretionary Housing Payment if you receive Housing Benefit and still have a shortfall; check the rules on GOV.UK or get help from Citizens Advice.