Does the contract say that you are liable for cleaning?
If that is right then the condition it was in at the outset is relevant.
Some contracts do purport to make you liable for the cost of deep cleaning.
If the contract goes no further than saying it has to be in the condition it was in when you took it over then they need to prove the condition it was in then and the deterioration.
They won't get away with making you pay to improve upon the property.
HOwever, I suppose you would have to sue to challenge that. They will deduct it from your deposit anyway. You could complain to the scheme if this is an AST.
Can I clarify anything for you?
If you didn't complain at the outset about the condition of the property then it will be difficult to claim damages now.
In principle you could bring a claim but a year after you move in it is not going to succeed in practice.