Affidavit (eidesstattliche Erklärung). Germany. Should I sign it?

Alright ive ordered a game for like €60 from ebay.de (from a large German game store, the have like 20000 references).
They delivered per DHL, i signed with my actual signature.

Then I called the store and said I still dont have the parcel although the tracking says the parcel has been handed over and signed.

(probably i should have said there was no game inside).

Now they send me this eidesstattliche Erklärung so I should sign it (that Ive never received the parcel or there was no game in it, there are like several options to choose from).

Should I sign or should I just forget about this refund? Are there gonna be any legal actions if they would obviously detect a fraud attempt? or ive got nothing to loose?

I live in Germany and i Ordered from a german store so its inside one country