Am I entitled to claim child tax credits back help please :)

Bev+4

Hi, I would be so grateful for any help. When I rang in my child tax credit in June the person who I was speaking to queried an amount that I put down as other income. Since child tax began I have been declaring nearly £1500 a year as other income as it came from a friendly society as I am disabled and not able to work. This person said did I need to declare it and I said that in the past I had asked and they had said I did. They suggested I rang the tax office to check and I found out that I infact should not have been declaring it and its not taxable which is great news as makes a difference to my award. My question is will they back date it and for how long, as I have been declaring this since 2003 as far as I can make out. I am waiting for them to get back to me but its taking its time and I want to know what rights I have. Thanks very much for any advice.