Hi,
I hope I can offer some constructive advice on this for you.
First of all you need to work out how much you can realistically afford to repay if this is your intention. I owed a similar amount to yourself and wrote (via email) to paydayexpress customer services and collections (email addresses are on the site) advising I was unable to repay the full amount on the due date owing to a change in personal circumstances and that I requested the removal of the CPA from my account.
I proposed to repay £100 a month on an outstanding amount of £700.
You will have to speak with the advisors at PDE over the phone at the time the date is due for your payment - my advice would be to withdraw all funds you have in the account you intend to make the payments from as they will more than likely attempt to take the payments on your due date.
Speak with them - in all honesty if you are reasonable with them and are making a proposal to repay your debt then they will work with you. You can request to have the interest frozen which will generally be met - again if you show integrity.
The key part of the advice is to request what they agree with you in writing, whether that be via email or in the post.
If you need a copy of the letter to send to them to make the request I can post this in here for you.
I know these things can be a massive worry when you've got into a fix but as long as you communicate with them, they will show compassion with your situation. Good luck and please feel free to ask any further questions you may need answers to.