thank you! I am stil very worried about contacting them, it might rock the boat, I am worried that they will demand the full amount back in one go. I will have to work up the courage!
@misscph1973
Hi 
Hey it's OK. They won't demand it all at once. What you owe is a separate issue. Your monthly instalments will stay the same. Tell them you are happy to keep paying the instalments as you are doing, but you wish to close your claim, and do not wish to receive anymore 'renewal of your tax credits' claims.
Good luck and I hope you manage to pay off what you owe. I am not even sure how much we owe now. About £500 probably!!! 
They never let us know, or sent a statement or anything!!! If I want to know, I have to phone them!
They are twats and it's a disgrace that they allow people to get into such financial difficulty. However, when you call them to offer to pay, they are more than happy to accept instalments. (Not sure how long is the longest they give you, but ours is 30 months.)
As someone mentioned earlier, I don't 'get' how they can't put tax credits with PAYE. Like let's say your weekly income is £288 and they figure you can have £44 tax credits a week (based on that figure.) If your wage rises to £298 one week, then drop the tax credits to £34 that week. If it's £300, drop the tax credits it to £32 that week IYSWIM. Surely it can't be that hard! They do it with national insurance, income tax, your pension etc.... 
This thread is horrendous as it has so many horror stories, but it's also brilliant, as it is providing huge support and hugs, and letting people know they are not alone.
Agree with @HelenaDove, funny how this thread is not being picked up by the papers/media, but they're all over a a thread entitled 'I think my husband has spent the night with his 18 year old secretary.'
Twats. 