Yes, write to Grabbey National direct asking for documentation in view of the pending court case threatened by DLA in their letter of xx (copy enclosed). Put a copy of DLA's threat in the letter to Grabbey and copy the letter to DLA too.(posted 8457 days ago)By doing this you are making sure they have been requested to play by the Civil Procedure rules.
Separately, serve a DPA Subject Access Rights notice on Grabbey. It may help you gather more info when you receive the probably inevitable refusal for docs from Grabbey.
Lee