Please relax about ''Court''!!
You've been reading too much of their own garbage on their websites.
And you can most definitely ignore the rubbish they print on their letters, it's all very cleverly designed psychological mumbo jumbo, printed by a computer.
You ignore them for as long as they fail to send you what you demanded, and then it must be enforceable or you can continue to ignore.
The time to sue / ask for rent reduction started when you became aware of the issue (that is 10 years ago). You are absolutely unable to claim for anything for more than 6 years ago, as it is 'statute barred'.
As for claiming anything within the last 6 years, if you have left it this long, expect the LL to claim that you accepted the error. If you wished to claim, you should have done so well before now. Expect them to claim that you accepted it, and are onl;y now claiming different as a result of their claim. You'd then have to persuade a judge otherwise.
Don't touch them owe me £500 since January 2019 make excuse after excuse. Seem they always have software problems sending money out. Keep saying they will call back or email nothing been chasing it now for 6 mths the phone staff always have the same banter we will chase it up and get back to you then nothing!