Application for Decree Nisi refused - Respondent disputing costs

[VirgoGrr]

I have sent in my application for Decree Nisi and have had a letter back saying:

Please note that the District Judge having considered the evidence filed, is not satisfied the the Petitioner is entitled to the decree sought, because:
The Petitioner seeks a costs order. The Respondent says costs have been agreed and he therefore objects to a costs order. The Petitioner to clarify whether or not costs have been agreed.
The Petitioner should deal with the matters above and renew the request for directions for trial.

The reason for this is that I have requested for him to pay the costs and on his Acknowledgement of Service form, he has said that we have a prior agreement that he would not pay costs. We did discuss this, but other factors have changed in relation to finances, so this agreement no longer stands.
The court has not sent back any of my forms - do I have to fill in and submit my application again or are they just wanting me to write a letter to say that I am still seeking a costs order? I understand that it's usual for the costs order to be awarded against the Respondent for Unreasonable Behaviour?