Child Tax Credits Suspended

Hi I'm after a little bit of advice, I have had my child tax credits suspended,the reason being was because apparently they said they had sent me a letter out in February,but then they said they sent me a letter out in January, And that I never replied to it, even tho the reason for that was because I never received any letter from them. So now I have had no money for 2 weeks, I'm a single parent of two children and I live with my father who is a pensioner. Just wondering if there is any help I can get towards me receiving any kind of money thanks.