I am unhappy with the decision made by the DWP, what can I do?

You should ask for a mandatory reconsideration. When requesting the reconsideration you should clearly state why you are disputing the decision and if possible send in supporting evidence.

If you're not happy with the outcome of the reconsideration, you can appeal to Her Majesty’s Courts and Tribunals Service (HMCTS). A tribunal panel will make a decision based on the facts and law. You can request either a paper or oral hearing. An oral hearing will normally be held at a venue near you where you and your representative will have the opportunity to present your case. Oral hearings have a higher success rate.

Normally you have one month from the decision to request a mandatory reconsideration or an appeal . It is important to appeal in time otherwise you might lose the chance to challenge the decision. If you miss the deadline, a late request can be made if you have good reasons is accepted why it’s late.

https://www.citizensadvice.org.uk/benefits/benefits-introduction/problems-with-benefits-and-tax-credits/challenging-benefit-decisions/challenging-a-decision-by-the-dwp-or-hmrc/