Tax Credits for the tax year 2012-13

I submitted this enquiry on 14-10-24 and again on 16-10-24, but have had no reply and cannot see the thread online. I have a TC3MM letter dated 11-10-24 about tax credits for the tax year 2012-13. This long after then, I'm concerned this may be a scam? If not, why would I receive such a letter without any prompt from me please? An amount of nearly £4,000 is mentioned - I can't tell if this refers to what I have been previously paid or if it is an amount which may be due to me. I have tried to find out about this by calling 0345 300 3900 but gave up after being on hold for a very long time. Will appreciate any advice/guidance please.

Hi,
The TC3MM is a letter sent from HMRC to customers who have a tax credit claim but one of the tax years was not finalised correctly at the end of the tax year. The tax years can be several years old.
We ask the customer to check that their personal circumstances were correct and the income was correct for the relevant tax year.
If the details shown are correct the customer does not need to do anything. If anything is incorrect the customer must tell us. If we find that the customer has not received their full entitlement we will pay any underpayments into their bank account.
Thank you.