Keep copies of the rent review notice, tenancy agreement, messages and any evidence of the previous rent or comparable properties. Ask the landlord in writing to explain how the increase was calculated and check the current rules and RTB guidance, as rent-control requirements can change. Do not simply stop paying rent; instead, contact the Residential Tenancies Board about dispute resolution if the issue is not resolved. The RTB will assess the facts and evidence, while a solicitor can advise you on a specific legal position.