Refund issue - Massimo Dutti through Zalando

[BlueMoonAndRedNose]

I bought 4 Massimo Dutti blazers through Zalando. Three arrived in one box, one in another. None fit, so I returned them immediately just as they arrived, 3 in one box, one in the other. I have two receips from the post office and evidence that both have been delivered. Yet Zalando have only refunded 3 blazers, so just one of the parcels.
What are my rights here if they say the 4th blazer hasn't arrived?
I have sent them copies of the receipts and screenshots of the delivery confirmation, but now they're ignoring me.

How long has it been since you emailed? This happened to be before with another store. One package had been processed for refund and the other hadn't been acknowledged it had been received. They emailed me after a few days of me enquiring about it and said sometimes packages are sent to different warehouses so would take longer or something. Anyway that refund came through a week or so later. Perhaps call their customer service instead? If you have your receipt it will be fine.