Many people have been overpaid tax credits
The tax credit system has been criticised for "completely unacceptable" errors, with one third of recipient families having been overpaid, according to a new report.
Many people in receipt of tax credit have told the BBC News website that they are still having problems - and are becoming increasingly frustrated and, in some cases, even desperate.
BBC News website offers some guidance.
I've been overpaid. What should I do?
If you have been overpaid, and expect your income for the current tax year to rise by more than £2,500, you must tell the HMRC.
But in the 2005 pre-Budget report it was announced that this threshold would rise to £25,000 in 2006.
You can either contact the tax credit helpline or write in to: HM Revenue & Customs Tax Credits, Comben House, Farriers Way, Netherton, L69 1BY.
The tax credit helpline number is 0845 300 3900.
You must also tell HMRC about a number of other changes in circumstance.
More details are available in WTC2 - Child Tax Credit and Working Tax Credit - A Guide, available on the HMRC's website.
I'm worried about debt. Where can I turn?
If you are worried about debt, there are a number of free debt advice agencies which can help you.
Try Consumer Credit Counselling Service (0800 1381111), National Debtline (0808 8084000) or Citizens Advice (020 7833 2181).
I want compensation for extra costs. I have got a query which can't wait, and I can't get through to the helpline?
The government has told BBC News that it will not set up a separate compensation scheme for tax credits.
2. Local Director
3. Adjudicators' Office
4. Parliamentary Ombudsman
Instead, claims will be processed through the Revenue's standard complaints procedure.
The compensation scheme is not well publicised.
However, it could be a lifeline to people who have incurred extra costs, such as financial charges or telephone costs as a result of mistakes made by the HMRC.
The HMRC can also offer compensation for worry and distress if it can be proved that mistakes and delays have caused a "great deal of inconvenience or irritation".
In addition, it could pay out if it handled a complaint badly or took an unreasonable time to deal with it.
Payments tend to range between £25 and £500 in these two categories.
Remember that payments are not automatic - and it will be up to the Revenue to decide on whether your case is valid.
If you want to complain, you need to download a copy of Code of Practice 1, can be found under the site index or the "Leaflets and Booklets" section on the Revenue's website.
I need my tax credit money urgently - and haven't received it yet. How can I get it?
If your money has not arrived, the HM Revenue & Customs (HMRC) is advising people to go down to their local inquiry centre - and try and get an emergency payment.
You can find out about where the office is on the HMRC website (see link on right).
You need to take your awards notice with you.
If you haven't received it yet, you should take confirmation of your national insurance number, such as an NI card or payslip.
In these cases, assessment will be based on individual circumstances, the HMRC said, and hardship.
Be prepared for a patient wait, though. Most tax offices are still extremely busy handling similar queries.
I have got a query which can't wait, and I can't get through to the helpline?
You could go down to your local HMRC Inquiry Centre.
Location details are on the HMRC's website (see link).
Take your awards notice with you. If you haven't received it yet, you should take confirmation of your national insurance number, such as an NI card or payslip.
Alternatively, you could contact your MP.
MPs and their researchers have their own little-known-about "tax credit" hotline to help constituents with complaints.
By contacting your MP you can effectively fast track your query.
You can find out how to contact your MP via the link on the right, through the parliament website, or by dialling the House of Commons switchboard on 020 7219 3000, and asking for the MP's office.
If you have problems with your MP not responding to your queries, you should address your complaint to the party's headquarters.
I'm being underpaid. How can I get more credit?/CPS:STYLE>
Your tax credit payment is currently based on your income two years' ago.
This means some people will be missing out, because their income has dropped, for example, through a change in circumstance, such as redundancy.
The Revenue says contacting the helpline is the best route, but if people can not get through, they should visit their local enquiry centre.
For more details see WTC2 - Child Tax Credit and Working Tax Credit - A Guide, available on the HMRC's website.