It seems you are on a fixed term 1 year contract, in which case it is correct that you cannot give notice to end the contract during the year. However, you do not have to give notice if you intend to leave at the end of the year. You just don't sign any new contract. It would be better if you did give some notice so the landlord/agent know they will have to get a new tenant.
If you want to leave during the year you could try to negotiate an arrangement where the agent attempts to get a new tenant, & you accept responsibility for the rent up to the time a new tenant moves in. However, this could leave you paying the rent for several months after moving out if they find it difficult to get a new tenant (or don't bother to try while you are still paying).