If there is no break clause in your Lease then I'm afraid that you will not be able to terminate the lease any earlier than the fixed term. Lease can be negotiated on whatever terms the parties choose and just because the lease is short it did not preclude you from attempting to negotiate the inclusion of one. I'm sorry to say that there are no statutory provisions which implies a break clause and so you are a bit stuck here.
If the Lease allows you to assign or sublet I would investigate this as a possibility to get out of paying the rent.
If the car parking sport was designated to you in the lease but with the landlord retaining the ability to move you to another spot then they are free to do so. If they have used the spot for another lease then they should have allocated you a new spot. You should request a further spot for you to park.
That they have given the spot away is not a breach of such seriousness that you are permitted to terminate though. It is a breach of contract, but not a repudiatory breach of contract that would entitle you to treat the contract as at an end.
Sorry it could not be better news. My advice if there is no break clause is either to utilise any clause permitting you to assign or sublet or to attempt to negotiate a surrender of the lease with the landlord (they would probably require payment of a sum of money for this).
If you simply leave and do not pay the rent then in all probability they will forfeit the lease and sue you for the remaining rent and loss they suffer.
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