Yes, absolutely
do take the creditors on, even if you have debt management arrangements in place - I have arrangements with all bar Nationwide, and there's been no ill effect thus far.
Chances are the reason you're in a pickle is partly due to these charges, so I'm sure even the creditors would accept that if you could reduce your debts to them by the amount of charges they have added to your account, it would be in everyone's best interests.
Have no fear - there are plenty of folks on here who are on debt management plans who have reclaimed/are in the process of reclaiming their fees.
Go for it
