Hi Shruti,
You can try this approach -
1. Create a new dunning procedure (say WO) and configure one level as 01 (release to Merc). Set days in arreas as 0. As a part of the activity, you can create a FM to release to mercantile (preferably a copy of FKK_COLL_AGENCY_RELEASE_0350).
2. While creating write off statistical open item, in user exit (FQEVENT 0010/0030), you can assign dunning procedure WO at the statistical document level (fkkop-mahnv).
3. On the immediate next dunning run, will pick up the statistical document for dunning to WO - 01. And as a part of the activity the document would be released.
4. You will then have to run a submission job (FP03DM) to create the referral file for the agency.
Alternatively, you can set up release job FP03M and in the addition selection tab you can mention the dunning procedure WO and level 01. If required you can enhance events 1734, 5060 to specifically select the statistical items (exclude the original final invoice documents).
In that case you don't have to define anything in dunning activity of WO - 01.
Either way you would require a following submission job (FP03DM).
Hope it helps. Let us know how you go.
Regards,
Bodhisattwa