Working tax credit

A question about : Working tax credit

I have been on working tax credit since September, working 16 hours a week. getting Ј182 with ctc. At the beginning of January I started working 30 hours a week, I phoned them and the lady said the amount I get weekly would go up as I had the 30 hour a week element - it went up by 15p....
I have now gone back to 16 hours a week, phoned them on Monday, told them of the change, had a payment go in today and its almost Ј20 less than what I was originally getting...

I don't understand it all. Really worried about having to pay them back loads of money.

Any advice would be great. Thanks

Best answers:

• Tax credits is based on income as well as hours so more info would be needed on the figures you have been providing them. It is also based n what you earn in the tax year, not each week/month.
  What was your income for last tax year?
  Have you been giving them a new estimate for this tax year when you've reported your changes?
  Also have you had any one off payments?