Adding baby to tax credit claim

[notsure17]

So I claim tax credits based on my husbands wage. I didn't put our new baby on our claim when he was born ( he is now 8 months old) because I didn't think I could because of the new 'you can only claim for 2 children' rule
I didn't know that it affected only children from April 2017. I thought it already applied so I didn't put him on and when I asked for advice I was told the same. Now when I rang tax credits up today for a separate issue obviously one of the security questions was how any children I have so I said the amount of children I had obviously without thinking and then realised I should have only told her the ones I have in the claim then she asked why he wasn't put on the claim before and I told her I didn't think I could and she said at the moment you can put as many as you want on for now and I should write a letter to backdate from date he was born and she's now put him in the claim. Will they really backdate from when he's born? And is my reason legitimate? And how do I prove it was wrongly advised?

No, they won't backdate to when he was born, legally they can only backdate 30 days from the date you reported the change. You can appeal, but you won't get anywhere.

The only way you might be able to do something is if you can prove you asked HMRC for advice and they advised you incorrectly. Did you actually ring up to add him and they told you that you couldn't? If so, you can request copies of the call to get evidence and then you need them to revise your award due to something called 'official error'.

The helpline do give wrong advice, but I would be surprised they would get this wrong so far ahead of the actual change. When did you ring them and what did you actually say?

Sorry, my previous post should have said 1 month for backdating, not 30 days (30 days is for new claims)