If it turns out that your dp does owe this money (i.e. the contract wasn't terminated when you made a payment and they then went quiet), I can understand that, looking at your credit report, they can see other creditors being paid a larger sum.
What you could do is sit down and do a budget. Work out all your income and write down all your outgoings (excluding debts). Make sure you put a reasonable allowance for living expenses as you don't want to end up not being able to put food on the table because you miscalculated. Then you see what is left at the end.
You then have to do a pro rata calculation. This is worked out as follows:
amount of debt x amount available
---------
total amount of debt
For example, say you had debts of £200, £400 and £800, but only £200 available to pay it off. With the above calculation you would offer £28pm to the £200 creditor, £57 to the £400 creditor and £114 to the £800 creditor, totalling £199.
This way each creditor is receiving the same proportion of their debt as the other creditors. You need to get each creditor to agree to this. Most creditors will agree when they see that you are being fair and genuinely trying to pay off the debt. If some nasty company decides to go down the bankruptcy route, the court may not grant their application if they can see that you are making genuine efforts and are being reasonable.
As I say, this is something to think about once you've established if the money is still outstanding, rather than the company trying it on after having terminated the agreement.