self empoyed working tax credits stopped

i had a review letter 3 weeks ago requesting loads of info about my self employed work as well as lots of personal info like car insurance documents a list of my bills and debts owed bank statements etc so i gathered all the info they asked for and sent it sraight back with a letter with details of other things they may need to understand my self employed work. today i recieved my documents back with a cover letter saying "i have decided that you are not entitled to the working tax credits element. this is because you have not provided enough evidence to support active self employment." they also say i need to repay a years worth of overpayment. i rung the number on the letter to try and find out what other evidence i need to provide only to be told i had reached a call centre and needed a direct number to who was dealing with my claim which i havent got and the call centre wont give me. i tried ringing back and spoke to someone else who told me that my child tax was being reduced to repay the overpayment so my total tax credits have been now halved she also said she would get a complience officer to ring me back monday to try and sort out the evidence they need.
has any one else had this problem with tax credits or can anyone give me any advice.
thanks