Thanks for your message, and sorry to hear about these issues.
Normally, when a tenancy is signed then you cannot cancel it without the agreement of the landlord. However, you may be able to “unwind the contract”. The law is found in the Consumer Protection from Unfair Trading Regulations 2008. Trading practices, such as misleading actions/omissions that are deemed 'unfair' are prohibited under consumer protection law.
Misleading actions can be things such as the nature, or fitness for habitation of the property, providing an incorrect inventory of the property or omitting material information from the description of a property so that a prospective tenant is more likely to sign a tenancy agreement.
Breaches of consumer protection law may constitute a criminal offence, or may give rise to enforcement action so as a result you may be able to unwind the contract – which means cancelling the agreement or take court action.
If you rented it through an agency I would suggest reporting the matter to the redress scheme. Every agency should belong to one of two redress schemes. They are The Property Ombudsman https://www.tpos.co.uk/ and The Property Redress Scheme https://www.theprs.co.uk/ To find out which one they belong, please ask them, or check on their website.
If not, then you should speak to the landlord directly and tell him you wish to unwind the contract.