Question about Room05 Frieda

Hello Team Galaxus. Now I see that the 50x70 pillowcase is available separately? I ordered the duvet cover (160 x 210 cm, 65 x 100 cm) for my partner and myself a few weeks ago and now I would like to order the smaller pillowcase after all. In the shopping cart there is the info: The maximum order quantity of this item is 1. How can I get around this ? Thank you very much for your help. Mo