Don't accept that 48-hour excuse without verifying it first, because in Spain you have way more time than they told you. The legal deadline to return a defective product is two years from purchase, period. That comes from the European Directive and it's in the Consumer Goods Guarantee Law. The seller can't just make up shorter deadlines, so that "the deadline has passed" argument simply doesn't work legally if the product arrived damaged.
What you should do now is put it in writing. Send an email or message to the store (don't just talk in person) where you detail the defect, when you bought it, when you discovered it, and that you requested the return. Keep everything: receipts, photos of the damaged product, screenshots of the conversation. If the store keeps refusing, you can file a complaint with the consumer protection office in your autonomous community, and honestly that usually sorts things out fast because retailers hate dealing with those procedures.
One trick that not everyone knows: if you have your digital purchase receipt or the record of your account at the store, that's stronger than anything. Stores often back down when they see you have everything documented and know your rights. And one more thing: if it was by credit card or debit card, you can also ask your bank to investigate the claim if the store refuses. That's almost a sure win for you.