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hello my make is Alex and I will help you.
On what basis does the landlord want to change the contract?
they can't, the contract is clear you pay a sum up front them monthly payments thereafter.
There is a legally binding contract which they can't now change, if they do you could sue for breach of contract.
They are bound by the terms of the contract.
Can I clarify anything for you about this today please?
Happy to help