HMRC say that they will only look at another dispute if there is new evidence.
The reason for sending another dispute is to tell HMRC why you do not agree with their reasons. For example, if HMRC write to you and say that you didn't tell them about a change in your circumstances, your second dispute should tell HMRC when you think you told them about the change and ask them to listen to the phone call/find a copy of the letter.
Follow the guidance in How to write a dispute letter showing you how to write a dispute letter. Between step 3 and 4 you should tell HMRC why you do not agree with their decision. If you have any new evidence, tell HMRC about it.
If you have no new evidence, but believe that HMRC have ignored evidence that you have already sent them, you should send a second dispute as well as a complaint. You should tell them what evidence they have ignored and why you think it is important. Explain that they should treat it as new evidence because it has not been looked at before.
There is no limit on the number of times you can send a dispute but HMRC will not stop asking for the money while they make their decision. However, normally HMRC will not change the decision unless you provide new evidence or you can show that they did not consider some evidence that they already had.
HMRC phoned me to talk about my dispute
Sometimes HMRC will ring you to talk about your dispute. They may tell you what caused the overpayment and why they think you have to pay the money back. They may do this instead of writing to you. If this happens, you should ask them to send you the decision in writing as well. This will make it easier if you want to make a complaint.
My dispute was turned down and I have no new evidence. What can I do now?
If you still do not think you should have to pay back the money, you can complain to HMRC. For information about how to do this see How to complain - tax credits.
You might also want to take your reply letter to an adviser to ask them to check that HMRC’s explanation is correct and that there are no mistakes. See How to find an adviser - tax credits.
After you have used the complaints system at HMRC, you can ask for your case to be looked at by the Adjudicator and later the Parliamentary Ombudsman. However, both of these independent people will only check if HMRC have carried out their responsibilities and not acted unreasonably. See Further help - tax credits for details about how to contact the Adjudicator and Parliamentary Ombudsman.