Letter Received about Tax Credits Review (TC3MM)

I have an official looking letter that refers to a tax credits review for 2012-13. Why would this be happening in 2024 please? It's made me fear this could be a scam. If it is legitimate, I can't understand the intended outcome - it states that a decision will be made on 10-11-24 and refers to an amount of nearly £4,000 - but I can't tell if this is an amount already paid or one that is due to me. I have tried phoning 0345 300 3900, but gave up after being half and hour on hold. Please advise. Many thanks.

Hi,
HMRC may write to a customer where a particular claim for a single or multiple tax years have not been correctly finalised on system.
In these cases we will write to the customer to ask if the details we hold are correct so that we can make the necessary legal decision.
We may also ask the customer to provide income details to ensure that we have paid the correct entitlement.
Without sight of the letter we are unable to confirm if this is the case.
You therefore do need to call Tax credits: general enquiries so tha your record can be accessed.
Thank you