Tax credit

i have written to the tax credit people in order to stop paying my child tax credit as they awarded me in error,based on advice i got here,but they are still paying me .i need them to stop paying me the tax credits asap as i am going to apply for my ILR in a couple of weeks time.They are saying that they send a referral to their head office and it takes time before they act on it.does anyone have any experience of this?what can i do to make sure they stop them immediately,can anyone advise,and also what will i put on the form since,technically i am still in receipt of this benefit even though i have asked them to stop paying it.can i say i am not receipt of public funds,since i have written for them to be stopped and will they find out if i said so,how thorough are they when checking the form.i am not deceive them ,but if the time comes for me to apply for ILR and they still have not stopped paying them,what would be the best thing to do with regards to filling in the form.