one of your rights under gdpr is that you are entitled (free of charge) to a listing of all the data the other party has about you.
when you ask them about this listing this request itself becomes data the party has about you. it should therefore he included in the listing. (it is self referential, but that’s how it is).
if the information that you requested such a listing is missing from the data they provide in response to you request, they are in breach of gdpr rules. from them on you might want to file a complaint.
( I’ve no idea whether this would result in any meaningful compensation, if at all. but at least it should keep them busy.)